hwc: Reserve pipes for video layers first

There could be scenarios where the bottom layers are RGB, which could
take up all ViG pipes as well, leaving no pipes for videos. Using
mixed mode may not help if those RGB layers are updating, since GPU
will be continuously invoked.

This patch reserves pipes for videos instead of serial order.

Change-Id: Ia5e25294ecc18a54dc36923a930cb23914d9475b
1 file changed