mmc: sdhci-of-sparx5: Add Sparx5 SoC eMMC driver

This adds the eMMC driver for the Sparx5 SoC. It is based upon the
designware IP, but requires some extra initialization and quirks.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20200825081357.32354-3-lars.povlsen@microchip.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>