modules: camera: Shutter notify message support

The shutter callback timestamp should originate from the sensor itself,
since it knows exactly when the first line of the frame started
exposing.  However, as a fallback (or in the CPU-painting case) query
CLOCK_BOOTTIME instead.

Change-Id: Id57c05525e9c575d009b9deb96a69557fccac16b
2 files changed