irqchip: mpm: Add MPM GPIO as top level interrupt controller

As MPM GPIO is the parent of TLMM, MPM GPIO becomes top level interrupt
controller. So, it's no use to add the parent domain to MPM GPIO
controller. Remove parent domain and add MPM-GPIO to simple interrupt
domain.

Change-Id: I3633222ac49b6b5259b47ae9fb85b3c303f78c75
Signed-off-by: Raghavendra Kakarla <rkakarla@codeaurora.org>