ARM: da850-evm: Replace CMD_SF with CMD_MTD

This patch enables MTD and CMD_MTD and it works with SPI NOR,
so the older CMD_SF can be removed.

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/da850evm_defconfig b/configs/da850evm_defconfig
index dd0eb98..a161ad5 100644
--- a/configs/da850evm_defconfig
+++ b/configs/da850evm_defconfig
@@ -30,6 +30,8 @@
 CONFIG_CMD_DM=y
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_GPT is not set
+CONFIG_CMD_MTD=y
+# CONFIG_CMD_SF is not set
 # CONFIG_CMD_SETEXPR is not set
 # CONFIG_CMD_TIME is not set
 # CONFIG_CMD_EXT4 is not set