The driver implementation refers to env/mmc.c, the storage media
binding to block layer can use it(Nand/Nor Flash...).
Support configure:
- CONFIG_ENV_OFFSET
- CONFIG_ENV_SIZE
- CONFIG_ENV_OFFSET_REDUND (optional)
- CONFIG_ENV_SIZE_REDUND (optional)
- CONFIG_SYS_MMC_ENV_PART (optional)
Change-Id: Ibb16f0dd7af1331f454784968fbdc9002f4b769c
Signed-off-by: Joseph Chen <chenjh@rock-chips.com>