mfd: ab8500: allow AB9540 based devices to use ABX500 pinctrl

The old AB8500 GPIO driver has been un-BROKEN and converted into a
multi-platform pinctrl driver. If any AB9540 based devices wish to
request any GPIO pins that it offers, they can after this patch.

Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>