mmc: sdhci-omap: Add platform specific reset callback

The TRM (SPRUIC2C - January 2017 - Revised May 2018 [1]) forbids
assertion of data reset while tuning is happening. Implement a
platform specific callback that takes care of this condition.

[1] http://www.ti.com/lit/pdf/spruic2 Section 25.5.1.2.4

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