msm: vidc: cancel power collapse before venus command

Currently power collapse thread is canceled once the command is
written into interface queues. Venus may pick up this command and
starts working. When driver queries for PC_PREP, Venus immediately
returned without canceling current tasks. This makes driver to do
PC while Venus is still working. This results in unknown behavior.
So driver needs to make sure that it cancels the PC thread before
any command to Venus. If PC thread already scheduled, cmdq write
will wait till PC finishes and do power on before giving interrupt
to Venus.

Change-Id: I7e2af9b2aea6240b52857b920f2ce0c60b2040c3
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>
Signed-off-by: Ashray Kulkarni <ashrayk@codeaurora.org>