mmc: sdhci_am654: Add Initial Support for AM654 SDHCI driver

The host controllers on TI's AM654 SOCs are not compatible with
the phy and consumer model of the sdhci-of-arasan driver. It turns out
that for optimal operation at higher speeds, a special tuning procedure
needs to be implemented which involves configuration of platform
specific phy registers.

Therefore, branch out to a new sdhci_am654 driver and add the phy
register space with all phy configurations to it. Populate AM654
specific callbacks to sdhci_ops and add SDHCI_QUIRKS wherever
applicable.

Only add support for upto High Speed for SD card and upto DDR52 speed
mode for eMMC. Higher speeds will be added in subsequent patches.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>