mmc: sdhci-esdhc-imx: Remove non-DT stub

i.MX has been converted to a devicetree only platform, so remove
the non-DT stub for sdhci_esdhc_imx_probe_dt().

Also, make the driver depend on OF now.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210314230824.148969-1-festevam@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>