env_mmc: add support for redundant environment

This patch add support for storing the environment redundant on
mmc devices. Substantially it re-uses the logic from the NAND implementation,
that means using an incremental counter for marking newer data.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>
diff --git a/board/freescale/common/sdhc_boot.c b/board/freescale/common/sdhc_boot.c
index e432318..fd0e910 100644
--- a/board/freescale/common/sdhc_boot.c
+++ b/board/freescale/common/sdhc_boot.c
@@ -32,7 +32,7 @@
 #define ESDHC_BOOT_IMAGE_SIZE	0x48
 #define ESDHC_BOOT_IMAGE_ADDR	0x50
 
-int mmc_get_env_addr(struct mmc *mmc, u32 *env_addr)
+int mmc_get_env_addr(struct mmc *mmc, int copy, u32 *env_addr)
 {
 	u8 *tmp_buf;
 	u32 blklen, code_offset, code_len, n;