msm: vidc: Add v4l2 private ioctl support

Add v4l2 private ioctl support to send private data
and commands to driver to utilize video hardware
features which are not supported by v4l2 framework.

Change-Id: I7f3a183aad0ad923a03417a0340c316fd1e9c671
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>