msm: camera: Add separate mutex for different ioctls

Real time ioctls such as buffer operations and registers
configuration updates are timing critical. Other ioctls
such as ISP stream start/stop could take longer time to
finish because the ioctl blocks until the hardware
start/stop streaming completely. Using a separate mutex
will prevent real time operations from starving and
results in framedrop.

Change-Id: I3421b596bde53198ba4df7da9636441762c739db
Signed-off-by: Kevin Chan <ktchan@codeaurora.org>