libstagefright: mtk: Use vendor extensions to check if we should fixup cropping

For mediatek video codecs, validate that the current cropped rectangle
is valid and use the full frame size otherwise. This fixes a bug where
format changes in the same native window would preserve the previous
cropping and cause most of the image to be off-screen.

Change-Id: If56ca11453f5d2e04a4138b2efe28203f30ba569
Ticket: PORRIDGE-440