xen: Add support for platform device with id 5853:0002

According to
https://xenbits.xen.org/docs/unstable/man/xen-pci-device-reservations.7.html
the Xen Platform Device can either be 5853:0001 or 5853:0002.
Currently kernel only recognises 5853:0001. Add detection for 5853:0002.
Tested with XenServer and different machine templates.

Reviewed by: royger