msm: camera: Add support to query ISP ID

Where there are more than one ISP hardware available, v4l-subdev
nodes are created in the order in which it is probed. ISP hardware
has different capabilities. User space driver needs to differentiate
these hardware. Add support to return ISP id of particular v4l-subdev
node to user space driver. The ISP id comes from kernel dtsi node
which the ideal representation of ISP hardware.

Change-Id: Ica19c0264c5d6bdc8434c7232ea2f3e7bb72f4a1
Signed-off-by: Sreesudhan Ramakrish Ramkumar <srramku@codeaurora.org>