msm: vidc: Limit the session QP for HEVC encoder

For some use cases HEVC RC algorithm is deriving QP as
low as 1. This increases the encoded bit rate to very
high value. Hence limit the minimum QP value to 2.

CRs-Fixed: 817156
Change-Id: I3f5cc0e51203272657673563ca94dcbbb778fe01
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>