msm: camera: Add IRQ Router subdev implementation.

Add initial driver code for IRQ Router hardware.
It shall be implemented as a v4l2 subdevice of the
msm cam server node.
Add logic in msm cam server to request for irqs configured
to the IRQ Router, which can be individual or composite.
When the individual camera hardware cores interrupt,
the cam server receives them through the common interrupt
handler and dispatches them to to the respective hardware
core's v4l2 subdevice.
If the usecase demands that the interrupts from two
different hw cores be composited into a single interrupt,
(for eg: VFE and ISPIF), then the cam server stores this
configuration in its interrupt lookup table. When the
interrupt is triggered on the composited interrupt,
it is dispatched to the individual hardware cores
which have been composited into that interrupt.

Change-Id: Iaadd60cc24de9b5ba8d09a151474658902244d7b
Signed-off-by: Kiran Kumar H N <hurlisal@codeaurora.org>