arm: rmobile: replacement of common parts of config by rcar-gen2-common.h

Common part of config for lager, koelsch, alt and gose board will be able to
replace rcar-gen2-common.h.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>