cxl/region: Move cxl_trace_hpa() work to the region driver

cxl/region: Move cxl_trace_hpa() work to the region driver

This work belongs in the region driver as it is only useful with
CONFIG_CXL_REGION. Add a stub in core.h for when the region driver
is not built.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/183222631f11a43c5e6debc42ec22fe1bd4b818a.1714496730.git.alison.schofield@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>