am57xx_evm_defconfig: Enable YMODEM support

Enable CONFIG_SPL_YMODEM_SUPPORT to support UART boot

Signed-off-by: Yan Liu <yan-liu@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
diff --git a/configs/am57xx_evm_defconfig b/configs/am57xx_evm_defconfig
index 91293da..51dedc6 100644
--- a/configs/am57xx_evm_defconfig
+++ b/configs/am57xx_evm_defconfig
@@ -25,6 +25,7 @@
 # CONFIG_SPL_NAND_SUPPORT is not set
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SPL_SPI_LOAD=y
+CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_CMD_SPL=y
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set