mfd: pm8921: Implement irq_get_irqchip_state

Implement irq_chip->irq_get_irqchip_state to make it possible for PMIC
block drivers to access the IRQ real time status bits. The status bits
are used for various kinds of input signals, e.g. GPIO.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>