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/stm32mp15_basic_defconfig b/configs/stm32mp15_basic_defconfig
index 6df0935..be553ad 100644
--- a/configs/stm32mp15_basic_defconfig
+++ b/configs/stm32mp15_basic_defconfig
@@ -40,7 +40,7 @@
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_PARTITION=3
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_I2C=y
-CONFIG_SPL_MTD_SUPPORT=y
+CONFIG_SPL_MTD=y
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_POWER=y
 CONFIG_SPL_SPI_FLASH_MTD=y