SDL2: add bgrx pixel format

This patch adds support of b8g8r8x8 pixel format for SDL2.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-id: 20160517072848.4540.34695.stgit@PASHA-ISP
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/sdl2-2d.c

@@ -116,6 +116,9 @@ void sdl2_2d_switch(DisplayChangeListener *dcl,
     case PIXMAN_r8g8b8x8:
         format = SDL_PIXELFORMAT_RGBA8888;
         break;
+    case PIXMAN_b8g8r8x8:
+        format = SDL_PIXELFORMAT_BGRX8888;
+        break;
     default:
         g_assert_not_reached();
     }