cxl/region: Move find_cxl_root() to cxl_add_to_region()

cxl/region: Move find_cxl_root() to cxl_add_to_region()

When adding an endpoint to a region, the root port is determined
first. Move this directly into cxl_add_to_region(). This is in
preparation of the initialization of endpoints that iterates the port
hierarchy from the endpoint up to the root port.

As a side-effect the root argument is removed from the argument lists
of cxl_add_to_region() and related functions. Now, the endpoint is the
only parameter to add a region. This simplifies the function
interface.

Signed-off-by: Robert Richter <rrichter@amd.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: "Fabio M. De Francesco" <fabio.m.de.francesco@linux.intel.com>
Tested-by: Gregory Price <gourry@gourry.net>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20250509150700.2817697-8-rrichter@amd.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>