Provides a mechanism to pass new PCI device IDs to device drivers
at runtime, rather than relying only on a static compiled-in list
of supported IDs.

For each driver which has a pci_driver->probe routine, two things
are added: a probe_it file, and a dynamic_id directory.  In the
dynamic_id directory is a new file, new_id.

/sys/bus/pci/drivers/e100
|-- dynamic_id
|   `-- new_id
`-- probe_it

One may read the new_id file, which by default returns:
$ cat new_id
echo vendor device subvendor subdevice class classmask
where each field is a 32-bit value in ABCD (hex) format (no leading 0x).
Pass only as many fields as you need to override the defaults below.
Default vendor, device, subvendor, and subdevice fields
are set to FFFFFFFF (PCI_ANY_ID).
Default class and classmask fields are set to 0.

One may write new PCI device IDs into the new_id file:
echo "8086 1229" > new_id

which will cause a new device ID (sysfs name 0) to be added to the driver.

/sys/bus/pci/drivers/e100
|-- dynamic_id
|   |-- 0
|   `-- new_id
`-- probe_it

$ cat 0
00008086 00001229 ffffffff ffffffff 00000000 00000000

One can then cause the driver to probe for devices again.
echo 1 > probe_it

Individual device drivers may override the behavior of the new_id
file, for instance, if they need to also pass driver-specific
information.  Likewise, reading the individual dynamic ID files
can be overridden by the driver.

This also adds an existance test field to struct driver_attribute,
necessary because we only want the probe_it file to appear iff
struct pci_driver->probe is non-NULL.

The device probing routines in pci-driver.c are enhanced to scan
first the static list of IDs, then the dynamic list (if any).