seco-mx6: set env_is_mmc in defconfig

Env is planned to be taken from user partition of eMMC.
Disabled CONFIG_ENV_IS_IN_FAT and enabled CONFIG_ENV_IS_IN_MMC.
Updated env offset to match edgehog boards.

Signed-off-by: Mikhail Vanyulin <mikhail.vanyulin@rtsoft.de>

configs/seco-mx6_defconfig

@@ -4,7 +4,7 @@ CONFIG_SYS_TEXT_BASE=0x17800000
 CONFIG_SYS_MALLOC_F_LEN=0x4000
 CONFIG_TARGET_SECO_MX6=y
 CONFIG_ENV_SIZE=0x2000
-CONFIG_ENV_OFFSET=0
+CONFIG_ENV_OFFSET=0xc0000
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg"
 CONFIG_DEFAULT_DEVICE_TREE="imx6q-san"
 CONFIG_DEFAULT_FDT_FILE="imx6q-san.dtb"
@@ -28,10 +28,7 @@ CONFIG_DM_MDIO=y
 CONFIG_DM_MMC=y
 CONFIG_DM_THERMAL=y
 CONFIG_EFI_PARTITION=y
-CONFIG_ENV_IS_IN_FAT=y
-CONFIG_ENV_FAT_INTERFACE="mmc"
-CONFIG_ENV_FAT_DEVICE_AND_PART="3:2"
-CONFIG_ENV_FAT_FILE="uboot.env"
+CONFIG_ENV_IS_IN_MMC=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_FIT=y
 CONFIG_FSL_USDHC=y