env: Make mmc as default option for CONFIG_ENV_FAT_INTERFACE

All configs are using mmc as default fat interface. That's why make it
default for everybody.
The reason for this patch is to make it default for Xilinx Zynq platform
which is not listed there.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/env/Kconfig b/env/Kconfig
index 2d972a5..8ab7be1 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -404,8 +404,7 @@
 config ENV_FAT_INTERFACE
 	string "Name of the block device for the environment"
 	depends on ENV_IS_IN_FAT
-	default "mmc" if ARCH_SUNXI
-	default "mmc" if TI_COMMON_CMD_OPTIONS || ARCH_ZYNQMP || ARCH_AT91
+	default "mmc"
 	help
 	  Define this to a string that is the name of the block device.