mtd: Rename SPL_MTD_SUPPORT to SPL_MTD

Rename SPL_MTD_SUPPORT to SPL_MTD in order to match MTD. This allows using
CONFIG_IS_ENABLED to test for MTD support.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
diff --git a/configs/j721e_evm_r5_defconfig b/configs/j721e_evm_r5_defconfig
index e76ab59..55169bb 100644
--- a/configs/j721e_evm_r5_defconfig
+++ b/configs/j721e_evm_r5_defconfig
@@ -53,7 +53,7 @@
 CONFIG_SPL_FS_EXT4=y
 CONFIG_SPL_I2C=y
 CONFIG_SPL_DM_MAILBOX=y
-CONFIG_SPL_MTD_SUPPORT=y
+CONFIG_SPL_MTD=y
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_SPL_DM_RESET=y