msm: cam: Add basic framework for camera drivers

Add basic framework for camera drivers such as
initializing the sub devices, entities and registering
as v4l2 sub devices.

CRs-Fixed: 1108532
Change-Id: If8fa025807d233b3ea6c68a14943c8b841ab6b7c
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>
Signed-off-by: Harsh Shah <harshs@codeaurora.org>