msm: vidc: handle mappings for dynamic buffer mode

For dynamic buffer mode, map and register each
buffer during qbuf before sending to firmware,
instead of doing it during prepare_buf. Based on
the buffer ref count, the FBD from the firmware is
unmapped and released back to client or queued back
to firmware.

Change-Id: I91aaf80f0177bcf2e18d3d26b41f5ea131334579
Signed-off-by: Arun Menon <avmenon@codeaurora.org>