clk: at91: implement suspend/resume for the PMC irqchip

The irq line used by the PMC block is shared with several peripherals
including the init timer which is registering its handler with
IRQF_NO_SUSPEND.

Implement the appropriate suspend/resume callback for the PMC irqchip,
and inform irq core that PMC irq handler can be safely called while
the system is suspended by setting IRQF_COND_SUSPEND.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>