ARM: sunxi: Add the Allwinner A31 compatible to the machine definition

The Allwinner A31 is a quad-Cortex-A7 based SoC, which shares a lot of
IPs with the previous SoCs from Allwinner, like the PIO, I2C, UARTs,
timers, watchdog IPs, but also differs by dropping the WEMAC ethernet
controller and most notably dropping the in-house IRQ controller in
favor of a ARM GIC one.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
ARM: sun6i: Add restart code for the A31

The Allwinner A31 has a different watchdog, with a slightly different
register layout, that requires a different restart code.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
ARM: sunxi: Introduce Allwinner A20 support

The Allwinner A20 is a dual-core Cortex-A7-based SoC. It is
pin-compatible with the A10, and re-uses most of the IPs found in it,
plus some additional ones like a Gigabit Ethernet controller.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>