virtio-mem: enable virtio-mem on arm64 in Kconfig

As virtio-mem works on arm64, so enabled it here in Kconfig.

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

Author: jongwu

drivers/virtio/Kconfig

@@ -96,7 +96,7 @@ config VIRTIO_BALLOON
 config VIRTIO_MEM
 	tristate "Virtio mem driver"
 	default m
-	depends on X86_64
+	depends on X86_64 || ARM64
 	depends on VIRTIO
 	depends on MEMORY_HOTPLUG_SPARSE
 	depends on MEMORY_HOTREMOVE