irqchip: gic: skip cluster power collapse activities

On some architectures the gic is kept powered on throughout power
collapse. These architectures need not save and restore distributor and
cpu regisiters. Allow for skipping power collapse related activities by
creating a boolean flag and setting that via IRQCHIP_DECLARE's callback
function.

Change-Id: Ic178cb39b974dca794f50e3027074e0eca678e19
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>