In certain cases interrupt enablement will be delayed relative to when
the InterruptEnable bits are written.  One example of this is when
a GPIO's "debounce" logice is first enabled.  After enabling debounce,
there is a 900 us "warm up" period during which InterruptEnable[0]
(bit 11) will read as 0 despite being written 1.  During this time
InterruptSts will not be updated, nor will interrupts be delivered, even
if the GPIO's interrupt configuration has been written to the register.

To work around this delay, poll the InterruptEnable bits after setting
them to ensure interrupts have truly been enabled in hardware before
returning from the irq_enable handler.
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>