login: add rule for qemu's pci-bridge-seat

Qemu provides a separate pci-bridge exclusively for multi-seat setups.
The normal pci-pci bridge ("-device pci-bridge") has 1b36:0001. The new
pci-bridge-seat was specifically added to simplify guest-side
multiseat configuration.  It is identical to the normal pci-pci bridge,
except that it has a different id (1b36:000a) so we can match it and
configure multiseating automatically.

Make sure we always treat this as separate seat if we detect this, just
like other "Pluggable" devices.

(David: write commit-message)