mmc: fsl_esdhc: convert to use fsl_esdhc_get_cfg_common()

The fsl_esdhc_init() was actually to get configuration of mmc_config.
So rename it to fsl_esdhc_get_cfg_common() and make it common for both
DM_MMC and non-DM_MMC.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>