mmc: Add Marvell Xenon SDHCI controller driver

mmc: Add Marvell Xenon SDHCI controller driver

This driver implementes platform specific code for the Xenon SDHCI
controller which is integrated in the Marvell MVEBU Armada 37xx and
Armada 7k / 8K SoCs.

History:
This driver is ported from the Marvell U-Boot version 2015.01 which is
written by Victor Gu <[email protected]> with minor changes ported from
the Linux driver which is written by Ziji Hu <[email protected]>.

Signed-off-by: Stefan Roese <[email protected]>
Cc: Jaehoon Chung <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Reviewed-by: Jaehoon Chung <[email protected]>