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: I7989b51294efc10d56f483cf6bb67075179620ea
Signed-off-by: Meera Gande <mgande@codeaurora.org>