Hello,aldobiziak,
Please add a line in mx25_3stack.h file:
/*
* MMC Configs
* */
#ifdef CONFIG_CMD_MMC
#define CONFIG_MMC 1
#define CONFIG_GENERIC_MMC
#define CONFIG_IMX_MMC
#define CONFIG_SYS_FSL_ESDHC_NUM 2
#define CONFIG_SYS_FSL_ESDHC_ADDR 0
#define CONFIG_SYS_MMC_ENV_DEV 0
#define CONFIG_IMX_ESDHC_V1
#define CONFIG_DOS_PARTITION 1
#define CONFIG_CMD_FAT 1
#define CONFIG_BOOT_PARTITION_ACCESS
#endif
Try it ,please !
Regards,
Weidong