mmc: sdhci-pci-dwc-mshc: synopsys dwc mshc support

Synopsys has DWC MSHC controller on HPAS-DX platform connected using PCIe
interface with SD card slot and eMMC device slots. This patch is to
enable SD cards connected on this platform. As Clock generation logic
is implemented using MMCM module of HAPS-DX platform, we have separate
functions to control the MMCM to generate required clocks with respect
to speed mode.

Signed-off-by: Prabu Thangamuthu <prabu.t@synopsys.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>