arm64: allwinner: A100: add support for Allwinner Perf1 board

A100 perf1 is an Allwinner A100-based SBC, with the following features:

- 1GiB DDR3 DRAM
- AXP803 PMIC
- 2 USB 2.0 ports
- MicroSD slot and on-board eMMC module
- on-board Nand flash
- ···

Adds initial support for it, including UART and PMU.

Signed-off-by: Yangtao Li <frank@allwinnertech.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/30f4a3fc6ac84d05094e2c3b89d1dddc8ff6b7fc.1595572867.git.frank@allwinnertech.com