pinctrl: sunxi: move PIO_BASE into sunxi_gpio.h

pinctrl: sunxi: move PIO_BASE into sunxi_gpio.h

On the Allwinner platform we were describing a quite comprehensive
memory map in a per-SoC header unser arch/arm.
In the old days that was used by every driver, but nowadays it should
only be needed by SPL drivers (not using the DT). Many addresses in
there were never used, and some are not needed anymore.

To avoid a dependency on CPU specific headers in an arch specific
directory, move the definition of the pinctroller MMIO base address into
the sunxi_gpio.h header, because the SPL routines for GPIO should be the
only one needing this address.
This is a first step towards getting rid of cpu_sun[x]i.h completely,
and allows to remove the inclusion of that file from the sunxi_gpio.h
header.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>