drivers: renesas: ddr: Move to common

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

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Change-Id: I9aef73d3e9a027a127ce7483b72d339559866727
22 files changed