Memory devices may specify volatile only, persistent only, and
partitionable space which when added together result in a total capacity.

If Identify Memory Device.Partition Alignment != 0 the device supports
partitionable space.  This partitionable space can be split between
volatile and persistent space.  The total volatile and persistent sizes
are reported in Get Partition Info.  ie

	active volatile memory = volatile only + partitionable volatile
	active persistent memory = persistent only + partitionable persistent

Define cxl_mem_get_partition(), check for partitionable support, and use
cxl_mem_get_partition() if applicable.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>