qemu-arm: Enable DHCP distro target

When booting the QEMU virt machine with -net nic,model=e1000 we can already
support network boot just fine today.

So let's enable the default bootcmd to also evaluate DHCP responses properly.
That way we can enable network boot seamlessly with the virt target.

Signed-off-by: Alexander Graf <agraf@suse.de>

include/configs/qemu-arm.h

@@ -30,7 +30,8 @@
 #define CONFIG_ENV_SIZE				SZ_64K
 
 #define BOOT_TARGET_DEVICES(func) \
-	func(SCSI, scsi, 0)
+	func(SCSI, scsi, 0) \
+	func(DHCP, dhcp, na)
 
 #include <config_distro_bootcmd.h>