mmc: sh_sdhi: Add SDHI support

mmc: sh_sdhi: Add SDHI support

R-Car Gen3 series have four SD card interfaces (SDHI0 to SDHI3),
two of which can also be used as MMC interfaces (SDHI2 and SDHI3).
This adds High-speed mode SD clock frequency between 25MHz and 50MHz,
8bit/4bit bus width, high capacity and low voltage device support.

Signed-off-by: Kouei Abe <[email protected]>
Cc: Hiroyuki Yokoyama <[email protected]>
Cc: Nobuhiro Iwamatsu <[email protected]>
Cc: Jaehoon Chung <[email protected]>
Reviewed-by: Nobuhiro Iwamatsu <[email protected]>
Reviewed-by: Jaehoon Chung <[email protected]>