ARM: configs: keystone: Enable CONFIG_MMC_SDHCI_OMAP

Enable CONFIG_MMC_SDHCI_OMAP so that TI's K2G SoC
can use sdhci-omap driver for MMC/SD controller.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>