ARM: sunxi: support more Allwinner SoCs

ARM: sunxi: support more Allwinner SoCs

So far we only supported the Allwinner A20 SoC. Add support for most
of the other virtualization capable Allwinner SoCs by:
- supporting the watchdog in newer (sun8i) SoCs
- getting the watchdog address from DT
- adding compatible strings for other 32-bit SoCs
- adding compatible strings for 64-bit SoCs

As all 64-bit SoCs support system reset via PSCI, we don't use the
platform specific reset routine there. Should the 32-bit SoCs start to
properly support the PSCI 0.2 SYSTEM_RESET call, we will use it for them
automatically, as we try PSCI first, then fall back to platform reset.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>