In its current state the gpio-ab8500 driver looks after some GPIO
lines found on the AB8500 MFD chip. It also controls all of its
own IRQ handling for these GPIOs by inventing some virtual IRQs
and handing those out to sub-devices. There has been quite a bit
of controversy over this and it was a contributing factor to the
driver being marked as BROKEN in Mainline.

The reason for adopting this method was due to added complexity
in the hardware. Unusually, each GPIO has two separate IRQs
associated with it, one for a rising and a different one for a
falling interrupt. Using this method complicates matters further
because the GPIO IRQs are actually sandwiched between a bunch
of IRQs which are handled solely by the AB8500 core driver.

The best way for us to take this forward is to get rid of the
virtual IRQs and only hand out the rising IRQ lines. If a
sub-driver wishes to request a falling interrupt, they can do
so by requesting a rising line in the normal way. They just
have to add IRQ_TYPE_EDGE_FALLING or IRQ_TYPE_EDGE_BOTH, if
they require both in the flags. Then if a falling IRQ is
triggered, the AB8500 core driver will know how to handle the
added complexity accordingly. This should greatly simply things.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
[Augment to keep irq_base for a while (removed later)]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>