mmc: sdhci-pci: Use ACPI to get max frequency for Intel NI byt sdio

mmc: sdhci-pci: Use ACPI to get max frequency for Intel NI byt sdio

On NI 9037 boards the max SDIO frequency is limited by trace lengths
and other layout choices. The max SDIO frequency is stored in an ACPI
table.

The driver reads the ACPI entry MXFQ during sdio_probe_slot and sets the
f_max field of the host.

Signed-off-by: Nathan Sullivan <nathan.sullivan@ni.com>
Reviewed-by: Jaeden Amero <jaeden.amero@ni.com>
Reviewed-by: Josh Cartwright <joshc@ni.com>
Signed-off-by: Zach Brown <zach.brown@ni.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>