mfd: pm8xxx-irq: set mask on suspend flag

The pm8xxx irq controller doesn't have wakeup source configuration bits.
It relies on managing wakeup interrupts in software. The generic irq code
supports managing wakeup interrupts if the irq_chip is defined with
IRQCHP_MASK_ON_SUSPEND.

Update the pm8xxx irq controller to use IRQCHIP_MASK_ON_SUSPEND.

For a chip that implements IRQCHP_MASK_ON_SUSPEND a mask callback
is a must. This callback will be called when the system goes to
suspend on all non-wakeup interrupts.

CRs-Fixed: 303137
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>