mfd: pm8xxx: convert to v2 irq interfaces to support hierarchical IRQ chips

Convert the PM8XXX IRQ code to use the version 2 IRQ interface in order
to support hierarchical IRQ chips. This is necessary so that ssbi-gpio
can be setup as a hierarchical IRQ chip with PM8xxx as the parent. IRQ
chips in device tree should be usable from the start without having to
make an additional call to gpio[d]_to_irq() to get the proper IRQ on the
parent.

pm8821_irq_domain_ops and pm8821_irq_domain_map are removed by this
patch since the irq_chip is now contained in the pm_irq_data struct, and
that allows us to use a common IRQ mapping function.

This change was tested on an APQ8060 DragonBoard.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>