arm64: dts: bitmain: Add Sophon Egde board support

Add devicetree support for Sophon Edge board from Bitmain based on
BM1880 SoC. This board is one of the 96Boards Consumer and AI platform.
More information about this board can be found in 96Boards product page:

https://www.96boards.org/documentation/consumer/sophon-edge/

Only UART peripheral support is enabled for now.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>