Don't check the device ID. Instead, check the class, subclass and
programming I/F. New SoC designs have different device IDs, but
don't need special treatment. Consequently, we fail to probe and
attach for no other reason than not having added the device ID to
the code.

Bank on Freescale's sense of backward compatibility and assume
that if we find a host controller, we know how work with it.

This fixes detection of the PCI Express host controllers on
Freescale's QorIQ family of processors (P1, P2 and P4).