Since pins multiplexing, SDHC shares signals with IFC, with this patch:
To enable SDHC in case of NOR/NAND/SPI boot
   a) For temporary use case in runtime without reboot system
      run 'mux sdhc' in u-boot to validate SDHC with invalidating IFC.
   b) For long-term use case
      set 'esdhc' in hwconfig and save it.
To enable IFC in case of SD boot
   a) For temporary use case in runtime without reboot system
      run 'mux ifc' in u-boot to validate IFC with invalidating SDHC.
   b) For long-term use case
      set 'ifc' in hwconfig and save it.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>