pnp: add PNP resource range checking function

Add a PNP resource range check function, indicating whether a resource
has been assigned to any device.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
[apw@canonical.com: fixed up exports et al]
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Eric Anholt <eric@anholt.net>