arm:aspeed: use memdev for RAM

memory_region_allocate_system_memory() API is going away, so
replace it with memdev allocated MemoryRegion. The later is
initialized by generic code, so board only needs to opt in
to memdev scheme by providing
  MachineClass::default_ram_id
and using MachineState::ram instead of manually initializing
RAM memory region.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>

hw/arm/aspeed.c

@@ -35,7 +35,6 @@ static struct arm_boot_info aspeed_board_binfo = {
 struct AspeedBoardState {
     AspeedSoCState soc;
     MemoryRegion ram_container;
-    MemoryRegion ram;
     MemoryRegion max_ram;
 };
 
@@ -184,6 +183,7 @@ static void aspeed_machine_init(MachineState *machine)
 
     memory_region_init(&bmc->ram_container, NULL, "aspeed-ram-container",
                        UINT32_MAX);
+    memory_region_add_subregion(&bmc->ram_container, 0, machine->ram);
 
     object_initialize_child(OBJECT(machine), "soc", &bmc->soc,
                             (sizeof(bmc->soc)), amc->soc_name, &error_abort,
@@ -215,8 +215,6 @@ static void aspeed_machine_init(MachineState *machine)
     object_property_set_bool(OBJECT(&bmc->soc), true, "realized",
                              &error_fatal);
 
-    memory_region_allocate_system_memory(&bmc->ram, NULL, "ram", ram_size);
-    memory_region_add_subregion(&bmc->ram_container, 0, &bmc->ram);
     memory_region_add_subregion(get_system_memory(),
                                 sc->memmap[ASPEED_SDRAM],
                                 &bmc->ram_container);
@@ -393,6 +391,7 @@ static void aspeed_machine_class_init(ObjectClass *oc, void *data)
     mc->no_floppy = 1;
     mc->no_cdrom = 1;
     mc->no_parallel = 1;
+    mc->default_ram_id = "ram";
 }
 
 static void aspeed_machine_palmetto_class_init(ObjectClass *oc, void *data)