cxl: Add support for reading CXL switch CDAT table

cxl: Add support for reading CXL switch CDAT table

Add read_cdat_data() call in cxl_switch_port_probe() to allow
reading of CDAT data for CXL switches. read_cdat_data() needs
to be adjusted for the retrieving of the PCIe device depending
on if the passed in port is endpoint or switch.

Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/169713682855.2205276.6418370379144967443.stgit@djiang5-mobl3
Signed-off-by: Dan Williams <dan.j.williams@intel.com>