drivers: sdhc: Add driver support for xlnx SDHC

Add driver support for xlnx SD/EMMC host controller. The driver
currently support SD host controller version 3.0 and EMMC host
controller version 5.1. This driver functions with the SDHC subsystem to
perform operations on device.

Driver support both interrupt and polled mode data transfer. Uses ADMA2
to perform data transfer.

Signed-off-by: Paul Alvin <alvin.paulp@amd.com>