msm: fd: Add face detect engine speed support

Face detection engine can operate on different clock
rates based on requested usecase.
Driver have support for speed control but device tree
support was missing.
If we want to support different speed levels we need to define
them in device tree. Rate levels should be
defined in incremental manner starting from lower clock rate.

Change-Id: Ie17f8d43728b75a9313ca2947b6f42f6687d4667
Signed-off-by: Gjorgji Rosikopulos <grosik@codeaurora.org>