msm: vidc: Get the current performance level

This change supports client to get the current
performance level of the video driver via
IOCTL_GET_PERF_LEVEL. The current performance
level indicate the number of MBs per second
is being processed by video hardware.

Change-Id: Ic6f5b2b14e0d77bf801c4f857f8a0e20339c199f
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>