cxl/region: Support to calculate memory tier abstract distance

cxl/region: Support to calculate memory tier abstract distance

An abstract distance value must be assigned by the driver that makes
the memory available to the system. It reflects relative performance
and is used to place memory nodes backed by CXL regions in the appropriate
memory tiers allowing promotion/demotion within the existing memory tiering
mechanism.

The abstract distance is calculated based on the memory access latency
and bandwidth of CXL regions.

Signed-off-by: Huang, Ying <ying.huang@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://patch.msgid.link/20240618084639.1419629-3-ying.huang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>