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/am62ax_evm_r5_defconfig b/configs/am62ax_evm_r5_defconfig
index d52de8b..4070415 100644
--- a/configs/am62ax_evm_r5_defconfig
+++ b/configs/am62ax_evm_r5_defconfig
@@ -43,7 +43,7 @@
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x400
 CONFIG_SPL_DMA=y
 CONFIG_SPL_DM_MAILBOX=y
-CONFIG_SPL_MTD_SUPPORT=y
+CONFIG_SPL_MTD=y
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_DM_RESET=y
 CONFIG_SPL_POWER_DOMAIN=y