riscv: dts: thead: add sipeed Lichee Pi 4A board device tree

Sipeed's Lichee Pi 4A development board uses Lichee Module 4A core
module which is powered by T-HEAD's TH1520 SoC. Add minimal device
tree files for the core module and the development board.

Support basic uart/gpio/dmac drivers, so supports booting to a basic
shell.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>