ARM: rmobile: Merge prior-stage firmware DT fragment into U-Boot DT on Gen3

ARM: rmobile: Merge prior-stage firmware DT fragment into U-Boot DT on Gen3

The prior-stage firmware generates DT fragment containing the /firmware
node, /reserved-memory node and /memory@ nodes. Merge these nodes into
the U-Boot DT, so U-Boot can use this information.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>