Move the Allwinner kernels to use fdt_pinctrl. This will read the pin
configuration from the FDT data, then set the pins into the requested
state. As part of this the gpio controller now reports the correct number
of pins instead of returning the number of bank * 32.

To allow for a future consolidated kernel we add the SOC_ALLWINNER_A10 and
SOC_ALLWINNER_A20 kernel options. These need to be set as appropriate for
the SoC the kernel will boot on.

Submitted by: Emmanuel Vadot <manu@bidouilliste.com>
Differential Revision: https://reviews.freebsd.org/D5177