mmc: sdhci-esdhc: clean up register definitions

The eSDHC register definitions in header file were messy and confusing.
This patch is to clean up these definitions.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>