exo/clients: Use DRM_FORMAT_ARGB8888 for GBM buffers

DRM_FORMAT_ARGB8888 (which is B,G,R,A in memory order) matches the used
GL internal format and is also more widely supported by minigbm drivers.

Bug: 882825
Change-Id: I909ceb04172e4c7a97c97e9c94a36f3bb467053a
Reviewed-on: https://chromium-review.googlesource.com/1219387Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590340}

components/exo/wayland/clients/client_base.cc

@@ -284,7 +284,7 @@ std::unique_ptr<ScopedVkCommandPool> CreateVkCommandPool(
 
 ClientBase::InitParams::InitParams() {
 #if defined(USE_GBM)
-  drm_format = DRM_FORMAT_ABGR8888;
+  drm_format = DRM_FORMAT_ARGB8888;
   bo_usage = GBM_BO_USE_SCANOUT | GBM_BO_USE_RENDERING | GBM_BO_USE_TEXTURING;
 #endif
 }