staging: greybus: gpio: switch GPIO portions to use GPIOLIB_IRQCHIP

Convert the GPIO driver to use the GPIO irqchip library GPIOLIB_IRQCHIP instead of reimplementing the same.

---
Changes in v2:
- Retained irq.h and irqdomain.h headers.
- Dropped function gb_gpio_irqchip_add() and
called gpiochip_irqchip_add() from probe().
- Referred https://lkml.kernel.org/r/[email protected].

---
 drivers/staging/greybus/Kconfig |   1 +
 drivers/staging/greybus/gpio.c  | 184 ++++----------------------------
 2 files changed, 24 insertions(+), 161 deletions(-)

index ab096bcef98c..b571e4e8060b 100644
@@ -148,6 +148,7 @@ if GREYBUS_BRIDGED_PHY
 config GREYBUS_GPIO
 	tristate "Greybus GPIO Bridged PHY driver"
 	depends on GPIOLIB
+	select GPIOLIB_IRQCHIP
 	---help---
 	  Select this option if you have a device that follows the
 	  Greybus GPIO Bridged PHY Class specification.

2.17.1