ARM: dts: rmobile: Add SoC and board U-Boot DT extras

Add U-Boot DT extras for each SoC and board. This marks the required
nodes with u-boot,dm-pre-reloc to start clock and PRR early on while
avoiding modification of the DTs imported from Linux.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>