msm: vidc: Use vmap instead of kmap

Support for vmap has been added for DMA buffers. Use
vmap instead of kmap.

CRs-Fixed: 2214010
Change-Id: I6a92c481bf1a2cef4a0d6412cb08aab69e9cc9d0
Signed-off-by: Vaibhav Deshu Venkatesh <vdeshuve@codeaurora.org>