msm: vidc: Add check to handle no-VMEM case

Currently, for targets which do not have VMEM, video
driver consider it as error and video session fails.
Add check to consider cases for target which do not
have VMEM.

Change-Id: I3661955fa8e72927c9708fe00c5d0eb57e154d29
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>