switchtec: Add device IDs for additional Switchtec products

The switchtec driver also supports the PAX, PFXL and PFXI products which
have the same management interface.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kurt Schwemmer <kurt.schwemmer@microsemi.com>