memory-device: introduce separate config option

memory-device: introduce separate config option

Some architectures might support memory devices, while they don't
support DIMM/NVDIMM. So let's
- Rename CONFIG_MEM_HOTPLUG to CONFIG_MEM_DEVICE
- Introduce CONFIG_DIMM and use it similarly to CONFIG NVDIMM

CONFIG_DIMM and CONFIG_NVDIMM require CONFIG_MEM_DEVICE.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20181005092024.14344-7-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>