ARM: dts: rmobile: Add Renesas Ebisu board support

Basic support for the Renesas Ebisu board based on R-Car E3:
  - Memory,
  - Main crystal,
  - Serial console,

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[shimoda: rebase and add SPDX-License-Identifier]
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>