modesetting: Disable pageflipping when using a swcursor

The miPointerSpriteFunc swcursor code expects there to only be a single
framebuffer and when the cursor moves it will undo the damage of the
previous draw, potentially overwriting what ever is there in a new
framebuffer installed after a flip.

This leads to all kind of artifacts, so we need to disable pageflipping
when a swcursor is used.

The code for this has shamelessly been copied from the xf86-video-amdgpu
code.

Fixes: xorg/xserver#828

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
(cherry picked from commit 0aaac8d7)
Signed-off-by: Łukasz Spintzyk <lukasz.spintzyk@displaylink.com>
3 jobs for lspintzyk/sw_cursor_support_merge in 4 minutes and 43 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #2785985
debian-testing

00:00:26

 
  Build And Test
passed #2785986
autotools-build-and-test

00:04:17

passed #2785987
meson-build-and-test

00:01:36