randr: auto-bind of GPU is a config change

When a GPU is auto-bound adding more outputs to a screen, that needs to count
as a configuration change on that screen so that a WM listening for
RRScreenChangeNotify gets notified and handles it as a hotplug. This is
particularly for cases where the outputs are already connected. Otherwise
nothing might happen.

Issue #909 describes a real world case where plugging in a DisplayLink dock
with a monitor already connected is sometimes left inactive by GNOME. That
issue is a race, and requires adding a sleep(5); as the first thing in
NewGPUDeviceRequest() to reproduce reliably. With the sleep, the monitor in the
dock will never activate automatically. Add this fix over the sleep, and the
issue is gone.

This fix was originally developed on a branch replicating Ubuntu 19.04 patch
set based on xserver 1.20.4. Testing on master branch was impossible due to
xorg/xserver#910.

Closes: xorg/xserver#909

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
3 jobs for mr/hotplug-fix in 7 minutes and 7 seconds (queued for 1 second)
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debian-testing

00:01:03

 
  Build And Test
passed #1591796
autotools-build-and-test

00:06:04

passed #1591797
meson-build-and-test

00:02:03