mm-camera2:isp2: Add support for 12bit-plain16 raw format

VFE hardware is capable of handling 12 bit
plain16 raw image format. As this support
is not there in software, failure is returned
whenever the raw format is 12bit plain16.

Change-Id: Iceca409e33a19e5fe9e56dd563a535416bf7e107
Signed-off-by: VijayaKumar T M <vtmuni@codeaurora.org>