ARM: dts: cros-ec-keyboard: Add alternate keymap for KEY_LEFTMETA

On newer keyboards this key is in a different place. Add both options to
the keymap so that both new and old keyboards work.

Cc: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>