hw/loongarch/virt: Use machine_memory_devices_init()

Let's use our new helper. While at it, use VIRT_HIGHMEM_BASE.

Cc: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Cc: Song Gao <gaosong@loongson.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230623124553.400585-6-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

hw/loongarch/virt.c

@@ -857,8 +857,8 @@ static void loongarch_init(MachineState *machine)
 
     /* initialize device memory address space */
     if (machine->ram_size < machine->maxram_size) {
-        machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
         ram_addr_t device_mem_size = machine->maxram_size - machine->ram_size;
+        hwaddr device_mem_base;
 
         if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
             error_report("unsupported amount of memory slots: %"PRIu64,
@@ -873,14 +873,8 @@ static void loongarch_init(MachineState *machine)
             exit(EXIT_FAILURE);
         }
         /* device memory base is the top of high memory address. */
-        machine->device_memory->base = 0x90000000 + highram_size;
-        machine->device_memory->base =
-            ROUND_UP(machine->device_memory->base, 1 * GiB);
-
-        memory_region_init(&machine->device_memory->mr, OBJECT(lams),
-                           "device-memory", device_mem_size);
-        memory_region_add_subregion(address_space_mem, machine->device_memory->base,
-                                    &machine->device_memory->mr);
+        device_mem_base = ROUND_UP(VIRT_HIGHMEM_BASE + highram_size, 1 * GiB);
+        machine_memory_devices_init(machine, device_mem_base, device_mem_size);
     }
 
     /* Add isa io region */