riscv: qemu: Create a simple-bus driver for the soc node

To enumerate devices on the /soc/ node, create a "simple-bus"
driver to match "riscv-virtio-soc".

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup@brainfault.org>

arch/riscv/cpu/qemu/cpu.c

@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <dm.h>
 
 /*
  * cleanup_before_linux() is called just before we call linux
@@ -19,3 +20,16 @@ int cleanup_before_linux(void)
 
 	return 0;
 }
+
+/* To enumerate devices on the /soc/ node, create a "simple-bus" driver */
+static const struct udevice_id riscv_virtio_soc_ids[] = {
+	{ .compatible = "riscv-virtio-soc" },
+	{ }
+};
+
+U_BOOT_DRIVER(riscv_virtio_soc) = {
+	.name = "riscv_virtio_soc",
+	.id = UCLASS_SIMPLE_BUS,
+	.of_match = riscv_virtio_soc_ids,
+	.flags = DM_FLAG_PRE_RELOC,
+};