gpio: pl061: add support for wakeup configuration

The PL061 supports interrupts and those can be wakeup interrupts. We
need to provide support for configuring those interrupts as wakeup
sources.

This patch adds irq_set_wake callback for PL061 so that GPIO interrupts
can be configured as wakeup.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>