hw/riscv/sifive_u: Set the soc device tree node as a simple-bus

To allow Linux to ennumerate devices on the /soc/ node set it as a
"simple-bus".

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Michael Clark <mjc@sifive.com>

hw/riscv/sifive_u.c

@@ -97,7 +97,7 @@ static void create_fdt(SiFiveUState *s, const struct MemmapEntry *memmap,
 
     qemu_fdt_add_subnode(fdt, "/soc");
     qemu_fdt_setprop(fdt, "/soc", "ranges", NULL, 0);
-    qemu_fdt_setprop_string(fdt, "/soc", "compatible", "ucbbar,spike-bare-soc");
+    qemu_fdt_setprop_string(fdt, "/soc", "compatible", "simple-bus");
     qemu_fdt_setprop_cell(fdt, "/soc", "#size-cells", 0x2);
     qemu_fdt_setprop_cell(fdt, "/soc", "#address-cells", 0x2);