configs/qemu: enable dhcp on network interfaces

Enable dhcp networking for qemu configs considered good enough for
testing purposes.

This excludes:
arm_nuri - emulation doesn't seem 100% correct for networking.
ppc_virtex_ml507 - doesn't emulate networking.
sh4eb - emulation doesn't seem 100% correct for the NIC.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
diff --git a/configs/qemu_sh4_r2d_defconfig b/configs/qemu_sh4_r2d_defconfig
index 4366ab1..8197738 100644
--- a/configs/qemu_sh4_r2d_defconfig
+++ b/configs/qemu_sh4_r2d_defconfig
@@ -3,6 +3,7 @@
 BR2_sh4=y
 
 # System
+BR2_SYSTEM_DHCP="eth0"
 BR2_TARGET_GENERIC_GETTY_PORT="ttySC1"
 
 # Filesystem