irqchip: gic-v3: provide save and restore api

Provide api to save/restore GICD state for SPIs. SPI
configuration is restored for GICD_ICFGR, GICD_ISENABLER,
GICD_IPRIORITYR, GICD_IROUTER registers. Following is the
sequence for restore:

1. For SPIs, check whether any of GICD_ICFGR, GICD_ISENABLER,
   GICD_IPRIORITYR, GICD_IROUTER, current configuration is
   different from saved configuration.

For all irqs, with mismatched configurations,

2. Set GICD_ICENABLER and wait for its completion.

3. Restore any changed GICD_ICFGR, GICD_IPRIORITYR, GICD_IROUTER
   configurations.

4. Set GICD_ICACTIVER.

5. Set pending for the interrupt.

6. Enable interrupt and wait for its completion.

Change-Id: I31cd5eb8c3226dcdfd474bc88b91c1cb5ca909e6
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>