gpio: nomadik: extract GPIO platform driver from drivers/pinctrl/nomadik/

gpio: nomadik: extract GPIO platform driver from drivers/pinctrl/nomadik/

Previously, drivers/pinctrl/nomadik/pinctrl-nomadik.c registered two
platform drivers: pinctrl & GPIO. Move the GPIO aspect to the
drivers/gpio/ folder, as would be expected.

Both drivers are intertwined for a reason; pinctrl requires access to
GPIO registers for pinmuxing, pull-disable, disabling interrupts while
setting the muxing and wakeup control. Information sharing is done
through a shared array containing GPIO chips and a few helper
functions. That shared array is not touched from gpio-nomadik when
CONFIG_PINCTRL_NOMADIK is not defined.

Make no change to the code that moved into gpio-nomadik; there should be
no behavior change following. A few functions are shared and header
comments are added. Checkpatch warnings are addressed. NUM_BANKS is
renamed to NMK_MAX_BANKS.

It is supported to compile gpio-nomadik without pinctrl-nomadik. The
opposite is not true.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://lore.kernel.org/r/20240228-mbly-gpio-v2-6-3ba757474006@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>