Add Xenon eMMC/SD/SDIO host controller core functionality.
Add Xenon specific initialization process.
Add Xenon specific mmc_host_ops APIs.
Add Xenon specific register definitions.

Add CONFIG_MMC_SDHCI_XENON support in drivers/mmc/host/Kconfig.

Marvell Xenon SDHC conforms to SD Physical Layer Specification
Version 3.01 and is designed according to the guidelines provided
in the SD Host Controller Standard Specification Version 3.00.
Signed-off-by: NHu Ziji <huziji@marvell.com>
Signed-off-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>