Atom S12x0 CPUs are identified by the CPU host bridge ID. Add an override
table based on PCI IDs as well as code to detect it.

PCI access functions can now be called with PCI disabled, so unlike previous
attempts to use PCI IDs, the code no longer depends on it. If PCI is disabled,
the CPU will not be identified correctly. Since it is unlikely that anything
will work in this case, this is an acceptable limitation.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>