virtio_pci_legacy: Use the table BAR and PBA BAR from MSI-X cap

virtio_pci_legacy: Use the table BAR and PBA BAR from MSI-X cap

The MSI-X resource shouldn't be assumed to be always on BAR1.
The Virtio v1.1 Spec did not specify that MSI-X table and PBA BAR has to
be BAR1 either.

Approved by:	so
Security:	EN-21:15.virtio
Reported by:	Yuan Rui <number201724@me.com>
Reviewed by:	bryanv, jhb
Approved by:	philip (mentor)
Differential Revision:	https://reviews.freebsd.org/D28817

(cherry picked from commit faf9a4e9142a02c289ee543a6091bd4b925c6a63)
(cherry picked from commit 98740ead97c60caca1d7cb3e996108c75f499beb)