staging: greybus: shape up greybus GPIO

Greybus GPIO seems to reimplement the already existing generic
gpiolib irqchip. Also use gpiochip_get_data(). Also use

Cc: Viresh Kumar <>
Cc: Axel Haslam <>
Cc: Johan Hovold <>
Cc: Sandeep Patil <>
Cc: Rui Miguel Silva <>
Cc: Greg Kroah-Hartman <>
Signed-off-by: Linus Walleij <>
ChangeLog v2->v3:
- Rebased to v4.13.
ChangeLog v1->v2:
- Add the hunk adding select GPIOLIB_IRQCHIP to Kconfig,
  sorry for sending patches too late in the night.

Greybus folks: please look at this. I expect something like this
to be applied before migrating from staging, I can't test it
2 files changed