msm: vidc: Skip unsetting VMEM on firmware during power collapse

Unsetting and Setting VMEM during power collapse and power resume
respectively is an overhead, since VMEM address and size is fixed.

Change-Id: I8d29361ac5e111caa0c4c5ee08cd68b019052744
Signed-off-by: Arun Menon <avmenon@codeaurora.org>