video: msm: wfd: Allow client to specify multiple slices per frame

Adds support for V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE, ..._MAX_BYTES ,
..._MAX_MB controls which allow clients in specify the numbers of slices
in a frame in terms of bytes or macroblocks.

Change-Id: I5e4e5bd9ebbb7a00714cbcb331f350c538289641
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>