mmc: sdhci-omap: Add tuning support

MMC tuning procedure is required to support SD card
UHS1-SDR104 mode and EMMC HS200 mode.

SDR104/HS200 DLL Tuning Procedure for AM572x platform is mentioned
in Figure 25-51. SDR104/HS200 DLL Tuning Procedure of
AM572x Sitara Processors Silicon Revision 2.0, 1.1 TRM
(SPRUHZ6I - October 2014–Revised April 2017 [1]).

The tuning function sdhci_omap_execute_tuning() will only be
called by the MMC/SD core if the corresponding speed modes
are supported by the OMAP silicon which is set in the mmc
host "caps" field.

[1] -> http://www.ti.com/lit/ug/spruhz6i/spruhz6i.pdf



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