Use two HW cursor buffers per CRTC

Switch to the other buffer when xf86_config->cursor changes. Avoids
these issues possible when re-using the same buffer:

* The HW may intermittently display a mix of the old and new cursor
  images.
* If the hotspot changes, the HW may intermittently display the new
  cursor image at the location corresponding to the old image's hotspot.

Bugzilla: https://bugs.freedesktop.org/108832
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
12 jobs for cursor-double-buffer in 1 minute and 58 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Docker Image
passed #62379
debian-testing

00:00:22

 
  Build
passed #62382
xserver-1.13

00:00:29

passed #62383
xserver-1.14

00:00:30

passed #62384
xserver-1.15

00:00:30

passed #62385
xserver-1.16

00:00:29

passed #62386
xserver-1.17

00:00:31

passed #62387
xserver-1.18

00:00:29

passed #62388
xserver-1.18-clang

00:00:31

passed #62389
xserver-1.19

00:00:28

passed #62390
xserver-1.19-clang

00:00:30

passed #62380
xserver-1.20

00:00:38

passed #62381
xserver-1.20-clang

00:00:33