pinctrl: nomadik: depromote GPIO to subsystem_init()

We no longer have to do GPIO initialization before the
pinctrl initialization, instead we can initialize the pinctrl
portions of the driver first and then the GPIO. Thus we can
move GPIO initialization to a subsystem_initcall(), but
not yet to a device_initcall().

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>