ANDROID: irqchip/irq-gic-v3: Fixed gic_suspend() stub for !CONFIG_PM

When CONFIG_PM is not enabled, we will be getting a an unused function
warning:

drivers/irqchip/irq-gic-v3.c:1388:12: warning: 'gic_suspend' defined but not used [-Wunused-function]
 static int gic_suspend(void) { return 0; }
            ^~~~~~~~~~~

Fixes: 9d0ccb89 ("ANDROID: irqchip/irq-gic-v3: Add vendor hook for gic suspend")
Reported-by: Anand Gore <anand.gore@broadcom.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Change-Id: Iaae683f0871122eb424fbf4460ad551a67f91456