irqchip: renesas-intc-irqpin: Add minimal runtime PM support

This is just enough to let pm_clk_*() enable the functional clock, and
manage it for suspend/resume, if present.
Before, it was assumed enabled by the bootloader or reset state.

To prevent the clock from being disabled while the module is needed for
wake-up, implement irq_chip.irq_set_wake(), which increments/decrements
the clock's enable_count when needed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lkml.kernel.org/r/1410527720-18061-3-git-send-email-geert+renesas@glider.be
Signed-off-by: Jason Cooper <jason@lakedaemon.net>