backend-drm: Further checks to skip plane assignment to HW planes

Mode change from mixed-mode to renderer-only means we should no longer
try to place views in HW planes (as we composite everything into the
primary plane) thus we should avoid that whenever that happens.

In the same time we need to be able to place in mixed-mode/renderer-only
mode the cursor view into the cursor plane (if one is available).

This patch adds a further check to skip plane assignment when disabling
overlay support (when we switch to renderer-only mode), when drivers do
not have atomic-modeset or it has been disabled intentionally.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
3 jobs for fix-mixed-mode in 1 minute and 12 seconds (queued for 1 minute and 21 seconds)
Status Job ID Name Coverage
  Container Prep
passed #1005008
container_prep

00:00:17

 
  Build
passed #1005009
build-native-meson-default-options

00:00:55

passed #1005010
build-native-meson-no-gl-renderer

00:00:34