msm: gpio: separate the interrupt header

The current gpio driver exposes a single header inside the mach-msm
directory. The driver implements an interrupt controller also in
addition to being a gpio controller. Separate the header that defines
functions for interrupt controller activities.

Change-Id: Id443f4da55e3d32578038dc0aa505cde847b175d
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>