pinctrl: sunxi: move pinctrl code

pinctrl: sunxi: move pinctrl code

Move the existing sunxi-specific low level pinctrl routines from
arch/arm/mach-sunxi into the existing GPIO code under drivers/gpio, so
that the common code can be shared outside of arch/arm.

This also takes the opportunity to move some definitions from our
header file into the driver C file, as they are private to the driver
and are not needed elsewhere.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Tested-by: Samuel Holland <samuel@sholland.org>