cxl/pci: Store component register base in cxlds

cxl/pci: Store component register base in cxlds

In preparation for defining a cxl_port object to represent the decoder
resources of a memory expander capture the component register base
address.

The port driver uses the component register base to enumerate the HDM
Decoder Capability structure. Unlike other cxl_port objects the endpoint
port decodes from upstream SPA to downstream DPA rather than upstream
port to downstream port.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
[djbw: clarify changelog]
Link: https://lore.kernel.org/r/164375084181.484304.3919737667590006795.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>