kmsdrm: remove redundant modeset_pending flag

this variable was added in commit 2067a7db8e and
ultimately tracks if this is a surface's first present. checking if the current
bo is NULL provides the same functionality and cuts down on a redundant piece
of state potentially getting out of sync in the future

src/video/kmsdrm/SDL_kmsdrmopengles.c

@@ -141,28 +141,22 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
         return 0;
     }
 
-    /* Do we have a modeset pending? If so, configure the new mode on the CRTC.
+    if (!windata->bo) {
-       Has to be done before next pageflip issues, so the buffer with the
+        /* On the first swap, immediately present the new front buffer. Before
-       new size is big enough for preventing CRTC from reading out of bounds. */
+           drmModePageFlip can be used the CRTC has to be configured to use
-    if (dispdata->modeset_pending) {
+           the current connector and mode with drmModeSetCrtc */
-
         ret = KMSDRM_drmModeSetCrtc(viddata->drm_fd,
           dispdata->crtc->crtc_id, fb_info->fb_id, 0, 0,
           &dispdata->connector->connector_id, 1, &dispdata->mode);
 
-        dispdata->modeset_pending = SDL_FALSE;
-
         if (ret) {
             SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Could not set videomode on CRTC.");
             return 0;
         }
+    } else {
+        /* On subsequent swaps, queue the new front buffer to be flipped during
+           the next vertical blank
 
-        /* It's OK to return now if we have done a drmModeSetCrtc(),
-           it has done the pageflip and blocked until it was done. */
-        return 1;
-    }
-
-    /* Issue pageflip on the next front buffer.
            Remember: drmModePageFlip() never blocks, it just issues the flip,
            which will be done during the next vblank, or immediately if
            we pass the DRM_MODE_PAGE_FLIP_ASYNC flag.
@@ -172,7 +166,6 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
            That makes it flip immediately, without waiting for the next vblank
            to do so, so even if we don't block on EGL, the flip will have completed
            when we get here again. */
-
         if (_this->egl_data->egl_swapinterval == 0 && viddata->async_pageflip_support) {
             flip_flags |= DRM_MODE_PAGE_FLIP_ASYNC;
         }
@@ -201,6 +194,7 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
                 return 0;
             }
         }
+    }
 
     return 1;
 }

src/video/kmsdrm/SDL_kmsdrmvideo.c

@@ -551,7 +551,6 @@ void KMSDRM_AddDisplay (_THIS, drmModeConnector *connector, drmModeRes *resource
 
     /* Initialize some of the members of the new display's driverdata
        to sane values. */
-    dispdata->modeset_pending = SDL_FALSE;
     dispdata->cursor_bo = NULL;
 
     /* Since we create and show the default cursor on KMSDRM_InitMouse(),
@@ -1073,7 +1072,6 @@ KMSDRM_SetDisplayMode(_THIS, SDL_VideoDisplay * display, SDL_DisplayMode * mode)
     /* Take note of the new mode to be set, and leave the CRTC modeset pending
        so it's done in SwapWindow. */
     dispdata->mode = conn->modes[modedata->mode_index];
-    dispdata->modeset_pending = SDL_TRUE; 
 
     for (i = 0; i < viddata->num_windows; i++) {
         SDL_Window *window = viddata->windows[i];
@@ -1256,9 +1254,6 @@ KMSDRM_CreateWindow(_THIS, SDL_Window * window)
             dispdata->mode = dispdata->original_mode;
         }
 
-        /* Take note to do the modesettng on the CRTC in SwapWindow. */
-        dispdata->modeset_pending = SDL_TRUE;
-
         /* Create the window surfaces with the size we have just chosen.
            Needs the window diverdata in place. */
         if ((ret = KMSDRM_CreateSurfaces(_this, window))) {
@@ -1348,7 +1343,6 @@ KMSDRM_ReconfigureWindow( _THIS, SDL_Window * window)
     /* Recreate the GBM (and EGL) surfaces, and mark the CRTC mode/fb setting
        as pending so it's done on SwapWindow.  */
     KMSDRM_CreateSurfaces(_this, window);
-    dispdata->modeset_pending = SDL_TRUE;
 
     /* Tell app about the size we have determined for the window,
        so SDL pre-scales to that size for us. */

src/video/kmsdrm/SDL_kmsdrmvideo.h

@@ -80,8 +80,6 @@ typedef struct SDL_DisplayData
     uint64_t cursor_w, cursor_h;
 
     SDL_bool default_cursor_init;
-    SDL_bool modeset_pending;
-
 } SDL_DisplayData;
 
 typedef struct SDL_WindowData