mmc: sdhci-omap: Add OMAP SDHCI driver

Create a new sdhci-omap driver to configure the eMMC/SD/SDIO controller
in TI's OMAP SoCs making use of the SDHCI core library. For OMAP specific
configurations, populate sdhci_ops with OMAP specific callbacks and use
SDHCI quirks.
Enable only high speed mode for both SD and eMMC here and add other
UHS mode support later.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>