hw/arm/virt: Use machine_memory_devices_init()

Let's use our new helper. We'll add the subregion to system RAM now
earlier. That shouldn't matter, because the system RAM memory region should
already be alive at that point.

Cc: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230623124553.400585-4-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

hw/arm/virt.c

@@ -1813,10 +1813,7 @@ static void virt_set_memmap(VirtMachineState *vms, int pa_bits)
     virt_set_high_memmap(vms, base, pa_bits);
 
     if (device_memory_size > 0) {
-        ms->device_memory = g_malloc0(sizeof(*ms->device_memory));
-        ms->device_memory->base = device_memory_base;
-        memory_region_init(&ms->device_memory->mr, OBJECT(vms),
-                           "device-memory", device_memory_size);
+        machine_memory_devices_init(ms, device_memory_base, device_memory_size);
     }
 }
 
@@ -2257,10 +2254,6 @@ static void machvirt_init(MachineState *machine)
 
     memory_region_add_subregion(sysmem, vms->memmap[VIRT_MEM].base,
                                 machine->ram);
-    if (machine->device_memory) {
-        memory_region_add_subregion(sysmem, machine->device_memory->base,
-                                    &machine->device_memory->mr);
-    }
 
     virt_flash_fdt(vms, sysmem, secure_sysmem ?: sysmem);