msm: vidc: Adds API to request performance level.

Adds API to request for a particular performance
level from video core. This is needed for Wi-fi
display (WFD) to reduce end to end latency.

Change-Id: Ib4133b8cd62ccad286be1984f944911754b887c5
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>
[davidb: Taking only videodev2.h part of patch]
Signed-off-by: David Brown <davidb@codeaurora.org>