Initial version of DTSI for ProXstream2 and PH1-LD6b and DTS for
PH1-LD6b reference board.
Import from Linux with some adjustments:
- Use SPDX-License-Identifier
- Add clock-frequency to serial nodes
- Drop unusable nodes from -ref.dts
While I am here, sort Makefile entries alphabetically.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
