drivers: renesas: Move plat common sources

Move plat common sources to common directory, so that same
code can be re-used by both R-Car Gen3 and RZ/G2 platforms.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Change-Id: Id2b1822c97cc50e3febaffc2e5f42b4d53809a17
5 files changed