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)

src/login/71-seat.rules.in

@@ -17,6 +17,11 @@ SUBSYSTEM=="usb", ATTR{bDeviceClass}=="09", TAG+="seat"
 # 'Plugable' USB hub, sound, network, graphics adapter
 SUBSYSTEM=="usb", ATTR{idVendor}=="2230", ATTR{idProduct}=="000[13]", ENV{ID_AUTOSEAT}="1"
 
+# qemu (version 2.4+) has a PCI-PCI bridge (-device pci-bridge-seat) to group
+# evices belonging to one seat. See:
+#     http://git.qemu.org/?p=qemu.git;a=blob;f=docs/multiseat.txt
+SUBSYSTEM=="pci", ATTR{vendor}=="0x1b36", ATTR{device}=="0x000a", TAG+="seat", ENV{ID_AUTOSEAT}="1"
+
 # Mimo 720, with integrated USB hub, displaylink graphics, and e2i
 # touchscreen. This device carries no proper VID/PID in the USB hub,
 # but it does carry good ID data in the graphics component, hence we