defconfig: dra74_evm: enable serial driver model

Enable serial driver model for dra74_evm as ns16550 supports
driver model.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/dra74_evm_defconfig b/configs/dra74_evm_defconfig
index 7bff294..394edbe 100644
--- a/configs/dra74_evm_defconfig
+++ b/configs/dra74_evm_defconfig
@@ -16,5 +16,6 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
 CONFIG_SPI_FLASH_SPANSION=y
+CONFIG_DM_SERIAL=y
 CONFIG_SYS_NS16550=y
 CONFIG_TI_QSPI=y