mmc: core: Export mmc_set_ios so that host drivers can use it

mmc_set_ios() is used by host drivers during suspend/resume
routines in indirect way i.e., by calling host->ops->set_ios().
But now with MMC_CLKGATE enabled, mmc_set_ios() also updates
host->clk_gated flag. So export this API so that host controller
drivers can use it.

Change-Id: Ib0c177635bb8d87ba68c98e08b8d940c73f2b80c
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>