mmc:host:sdhci-pci:Addition of Arasan PCI Controller with integrated phy.

The Arasan Controller is based on a FPGA platform and has integrated phy
with specific registers used during initialization and
management of different modes. The phy and the controller are integrated
and registers are very specific to Arasan.

Arasan being an IP provider, licenses these IPs to various companies for
integration of IP in custom SOCs. The custom SOCs define own register
map depending on how bits are tied inside the SOC for phy registers,
depending on SOC memory plan and hence will require own platform drivers.

If more details on phy registers are required, an interface document is
hosted at https://arasan.com/NF/eMMC5.1 PHY Programming in Linux.pdf.

Signed-off-by: Atul Garg <agarg@arasan.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>