drivers: sdhc: Cadence SDHC driver bug fixes and other improvements

* Internal Clock not getting stable during initialization
* SD clock was not enabled
* Removed duplicate file.
* Removed write to readonly registers
* Moved function pointer structure from data section to RO section
* Wrong macro names
* Refactoring of lower layer header file.

Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia@intel.com>