riscv: qemu: enable distro boot

Enable distro boot on the qemu-riscv32/64 boards. Supported boot target
devices are VirtIO and DHCP.

Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
diff --git a/configs/qemu-riscv32_defconfig b/configs/qemu-riscv32_defconfig
index b556443..6334d8c 100644
--- a/configs/qemu-riscv32_defconfig
+++ b/configs/qemu-riscv32_defconfig
@@ -1,7 +1,9 @@
 CONFIG_RISCV=y
 CONFIG_TARGET_QEMU_VIRT=y
+CONFIG_DISTRO_DEFAULTS=y
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_FIT=y
 CONFIG_DISPLAY_CPUINFO=y
 CONFIG_DISPLAY_BOARDINFO=y
+# CONFIG_CMD_MII is not set
 CONFIG_OF_PRIOR_STAGE=y