MMC: add sdhci generic framework

Nowdays, there are plenty of mmc driver in uboot adopt the sd standard
host design, aka as sdhci. It is better to centralize the common logic
together to better maintenance.

Signed-off-by: Lei Wen <leiwen@marvell.com>
Acked-by: Andy Fleming <afleming@freescale.com>
3 files changed