mmc: sdhci-esdhc-imx: factor out hw related initialization into function

Move all hw related static initializations into a separate function
which helps concentrate the hw related initialization code.
And that function could also be called by other places later as a
basic hw state restore.
e.g. suspend/resume where the hw state is possible to lost due to
low power mode.

Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>