drm/mediatek: Support reflect-x plane rotation

Add support for REFLECT_X rotations.

Cc: Fritz Koenig <frkoenig@chromium.org>
Cc: Daniele Castagna <dcastagna@chromium.org>
Cc: Miguel Casas <mcasas@chromium.org>
Cc: Mark Yacoub <markyacoub@google.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>