msm: vidc: change interface for opening driver instance

This change will ensure that vidc clients specify the
core id as venus or q6 to open a driver session.
Without this change, sometimes due to driver probe deferral,
core_id_0 would be taken by q6 and vidc clients intending to open a
venus decode session ended up opening a q6 decode session.

Change-Id: I4f9c862b8057999e4db7ca75be493138737a58a8
Signed-off-by: Arun Menon <avmenon@codeaurora.org>