pv-drivers: use PCI interfaces to request IO and MEM resources on platform device

pv-drivers: use PCI interfaces to request IO and MEM resources on platform device

This is the correct interface to use and something has broken the use
of the previous incorrect interface (which fails because the request
conflicts with the resources assigned for the PCI device itself
instead of nesting like the PCI interfaces do).

pci_request_region() has been available since at least Linux 2.6.5.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@novell.com>