ARM: rmobile: Enable support for OpTee on Gen3

Enable OpTee support on R-Car Gen3, so that U-Boot would copy the
OpTee /firmware and /reserved-memory nodes into the Linux DT.

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>