drm/mediatek: Turn off Alpha bit when plane format has no alpha

This change enables XR24 format to be displayed as an overlay on top of
the primary plane.

Suggested-by: Sean Paul <seanpaul@chromium.org>
To: CK Hu <ck.hu@mediatek.com>
To: dri-devel@lists.freedesktop.org
Cc: Daniele Castagna <dcastagna@chromium.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Mark Yacoub <markyacoub@google.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_disp_ovl.c

@@ -266,7 +266,7 @@ static void mtk_ovl_layer_config(struct mtk_ddp_comp *comp, unsigned int idx,
 	}
 
 	con = ovl_fmt_convert(ovl, fmt);
-	if (idx != 0)
+	if (state->base.fb->format->has_alpha)
 		con |= OVL_CON_AEN | OVL_CON_ALPHA;
 
 	if (pending->rotation & DRM_MODE_REFLECT_Y) {