mmc: sdhci-esdhc-imx: optimize the clock setting

When force clock off, check the SDOFF of register PRSSTAT to make sure
the clock is gate off. Before force clock on, check the SDSTB of register
PRSSTAT to make sure the clock is stable, this will eliminate the clock
glitch.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/1582100757-20683-2-git-send-email-haibo.chen@nxp.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>