msm-vidc: calculate encode output buffer size considering 10-bit

In case of opaque color format the bit depth will be known with
first ETB. Existing logic calculates output buffer size based on 
8-bit which won't be sufficient for 10-bit.
So consider 10-bit by default while calculating encoder output
buffer size. 

Change-Id: I51eee2fcb0dc137c596babd04659cd1fc087ebd6