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 <[email protected]>
Reviewed-by: David Gibson <[email protected]>
Acked-by: David Gibson <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
Message-Id: <20181005092024[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>