pinctrl: exynos: bind GPIO driver along with pinctrl

pinctrl: exynos: bind GPIO driver along with pinctrl

The devicetree of Samsung devices typically have the pin controller and
GPIO bank descriptors under the same pinctrl node. In U-Boot, these are
handled by two separate drivers. It is not possible to invoke both
drivers from a single node compatible.

Bind the GPIO driver on pinctrl driver bind, with the same OF node as
the pinctrl driver. This solution is already being used in other pinctrl
drivers. The hierarchy, as represented in `dm tree`, is as follows:

  pinctrl@13750000
  |-- gpio-banks
  |   |-- gpr0-gpio-bank
  |   |-- gpr1-gpio-bank
  |   |-- gpr2-gpio-bank
  |   |-- gpr3-gpio-bank
  |   `-- gpr4-gpio-bank
  |-- sd0-bus-width1-pins
  |-- sd0-bus-width4-pins
  |-- sd0-bus-width8-pins
  `-- sd0-clk-pins

Since a bind function doesn't exist, create and add it to all pinctrl
drivers.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>