msm: vidc: Allocate persist buffers.

Persist buffers are needed by decoder/encoder
in some cases. These buffers are mandatory and
cannot be ignored. This change allocates persist
buffers according to the requirement by video device
to avoid hangs.

Change-Id: I961bb1abe45dba1cbc770edef2277f33ea186546
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>