drm/amd/display: Expose DRM_FORMAT_RGB565 on overlay planes

RGB565 support isn't restricted to just the primary plane in DC, so
also expose support for it on overlays.
Signed-off-by: NNicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: NAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: NDavid Francis <david.francis@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4251,6 +4251,7 @@ static const uint32_t overlay_formats[] = {
 	DRM_FORMAT_RGBA8888,
 	DRM_FORMAT_XBGR8888,
 	DRM_FORMAT_ABGR8888,
+	DRM_FORMAT_RGB565
 };
 
 static const u32 cursor_formats[] = {