ARM: dts: rmobile: Extract SCIF2 node on E3 Ebisu

The SCIF2 node is not in Linux 4.17 DTs on E3, pull it into U-Boot
specific DT extras until it hits mainline Linux, to make syncing of
DTs easier.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
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V2: Rebase on u-boot/master