drivers: renesas: eMMC: Move to common

Move eMMC 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: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Change-Id: I7f3055709337327d1a1c9f563c14ad1626adb355
13 files changed