arm/dt: pm8644: Add GPIO and MPP devices for PMIC PM8644

The new dtsi files are arranged so that parameters can be
overriden in convenient ways. It contains the platform independent
characteristics for each of the PMIC devices.  This includes
the SPMI base register for each gpio and mpp devices, its name,
its compatible string, and its status.

Change-Id: I2a33eb60347b77f41f2b3473c25ae76ea29d7972
Signed-off-by: Ravi Kumar V <kumarrav@codeaurora.org>