MMC: Ingenic: Add support for 8bit mode and LPM and JZ4760 Soc

[Zhou Yanjie]

1.adjust the macro definition name to match the corresponding
  register name in the datasheet.
2.add support for 8bit mode, now supports 1bit/4bit/8bit modes.
3.add support for probing mmc driver on the JZ4760 Soc from Ingenic.
4.add support for Low Power Mode of Ingenic's MMC/SD Controller.