mmc: sdhci: Add host driver support to enable clock gating

Enable config MMC_CLKGATE to enable aggressive clock gating framework that
will disable clocks when the host is not in use for 200ms.

Change-Id: I6bef5dc18b561871689b3d730fd3486323b12520
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>