msm: vidc: Delay firmware unload during session close

Video driver loads and unloads firmware at the start
and end of each session. Firmware download takes up
to 100 msec. When there are many b2b video sessions
e.g. thumbnail generation, this is an unnecessary
overhead. To overcome this problem, video driver will
unload the firmware 10 secs after the session is closed.
If a new session starts during this period, it will not
be required to download the firmware again.

Change-Id: Ia515c3ed89c75ea9e43852958d1cbb2d77fe4c51
Signed-off-by: Arun Menon <avmenon@codeaurora.org>