vmrun.sh: allow device name arguments in pci-passthru option

This is more intuitive than having to run pciconf -l and figure out
the bus/slot/func entry manually.

Reviewed by: markj
Sponsored by; The FreeBSD Foundation
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43270

(cherry picked from commit 2ee77056d2d4f9d43bd316ce6dc91bf5e4b0848b)