arm64: dts: add LS1046A-RDB board support

The LS1046A reference design board (RDB) is a high-performance computing,
evaluation, and development platform that supports the LS1046A SoC.

Signed-off-by: Mingkai Hu <Mingkai.Hu@nxp.com>
Signed-off-by: Shaohui Xie <Shaohui.Xie@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>