msm: camara: sync: Add callback registration logic for synx

Synx driver is dependent on camera driver for registering callback
functions of sync driver. This change invert the logic, and camera
driver will register the callback functions for synx driver at the
time of sync driver probe.

Change-Id: I2dbee15ba4c7a9dde336a4bb1f2a4dddcd90348b
Signed-off-by: Jigarkumar Zala <jzala@codeaurora.org>