vidc: 1080p : Add support for skip frame in slice delivery mode

Slice delivery mode for H264 encoder will deliver constant number of
output slice buffers for each frame. In case of CBR rate control method,
core will skip frames to maintain the output quality, in which case
driver need to send out the output buffers with data length as zero
for skipped frame output type from the core.

CRs-fixed: 362356
Change-Id: I647092d802b95558422cf1537f3e8bf69cd68b1b
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>