input: keyboard: adp5588-keys: support gpi key events as 'gpio keys'

This change replaces the support for GPIs as key event generators.
Instead of reporting the events directly, we add a gpio based irqchip
so that these events can be consumed by keys defined in the gpio-keys
driver (as it's goal is indeed for keys on GPIOs capable of generating
interrupts). With this, the gpio-adp5588 driver can also be dropped.

The basic idea is that all the pins that are not being used as part of
the keymap matrix can be possibly requested as GPIOs by gpio-keys
(it's also fine to use these pins as plain interrupts though that's not
really the point).

Since the gpiochip now also has irqchip capabilities, we should only
remove it after we free the device interrupt (otherwise we could, in
theory, be handling GPIs interrupts while the gpiochip is concurrently
removed). Thus the call 'adp5588_gpio_add()' is moved and since the
setup phase also needs to come before making the gpios visible, we also
need to move 'adp5588_setup()'.

While at it, always select GPIOLIB so that we don't need to use #ifdef
guards.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>

drivers/input/keyboard/Kconfig

@@ -40,6 +40,8 @@ config KEYBOARD_ADP5520
 config KEYBOARD_ADP5588
 	tristate "ADP5588/87 I2C QWERTY Keypad and IO Expander"
 	depends on I2C
+	select GPIOLIB
+	select GPIOLIB_IRQCHIP
 	help
 	  Say Y here if you want to use a ADP5588/87 attached to your
 	  system I2C bus.