drm/amdgpu/dc: Require primary plane to be enabled whenever the CRTC is

Don't check drm_crtc_state::active for this either, per its
documentation in include/drm/drm_crtc.h:

 * Hence drivers must not consult @active in their various
 * &drm_mode_config_funcs.atomic_check callback to reject an atomic
 * commit.

atomic_remove_fb disables the CRTC as needed for disabling the primary
plane.

This prevents at least the following problems if the primary plane gets
disabled (e.g. due to destroying the FB assigned to the primary plane,
as happens e.g. with mutter in Wayland mode):

* The legacy cursor ioctl returned EINVAL for a non-0 cursor FB ID
  (which enables the cursor plane).
* If the cursor plane was enabled, changing the legacy DPMS property
  value from off to on returned EINVAL.

v2:
* Minor changes to code comment and commit log, per review feedback.

GitLab: https://gitlab.gnome.org/GNOME/mutter/-/issues/1108
GitLab: https://gitlab.gnome.org/GNOME/mutter/-/issues/1165
GitLab: https://gitlab.gnome.org/GNOME/mutter/-/issues/1344


Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>