uboot-airoha: use separate DTB for Nokia XG-040G-MD

CONFIG_OF_EMBED is intended for debugging and is not recommended for
production devices. Remove it from the Nokia XG-040G-MD defconfig so
Kconfig selects CONFIG_OF_SEPARATE, consistent with the other Airoha
boards.

The existing default device tree and u-boot.bin build target ensure that
the separate DTB is built and appended to the deployable U-Boot image.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>

package/boot/uboot-airoha/patches/401-add-nokia-xg-040g-md.patch

@@ -1,6 +1,6 @@
 --- /dev/null
 +++ b/configs/an7581_nokia_xg-040g-md_defconfig
-@@ -0,0 +1,134 @@
+@@ -0,0 +1,133 @@
 +CONFIG_ARM=y
 +CONFIG_ARCH_AIROHA=y
 +CONFIG_POSITION_INDEPENDENT=y
@@ -58,7 +58,6 @@
 +CONFIG_CMD_SMC=y
 +CONFIG_CMD_UBI=y
 +CONFIG_CMD_UBI_RENAME=y
-+CONFIG_OF_EMBED=y
 +CONFIG_ENV_OVERWRITE=y
 +CONFIG_ENV_IS_IN_UBI=y
 +CONFIG_ENV_REDUNDANT=y