Revert "Revert "drm/amd/display: Implement zpos property""

This reverts commit e2066eb4.

The problematic IGT test case (i.e. kms_atomic@plane-immutable-zpos) has
been fixed as of commit cb77add45011 ("tests/kms_atomic: remove zpos <
N-planes assert") to the IGT repo. So, reintroduce the reverted code.

Link: https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/commit/cb77add45011b129e21f3cb2a4089a73dde56179Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c

@@ -1468,6 +1468,15 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
 		drm_plane_create_blend_mode_property(plane, blend_caps);
 	}
 
+	if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
+		drm_plane_create_zpos_immutable_property(plane, 0);
+	} else if (plane->type == DRM_PLANE_TYPE_OVERLAY) {
+		unsigned int zpos = 1 + drm_plane_index(plane);
+		drm_plane_create_zpos_property(plane, zpos, 1, 254);
+	} else if (plane->type == DRM_PLANE_TYPE_CURSOR) {
+		drm_plane_create_zpos_immutable_property(plane, 255);
+	}
+
 	if (plane->type == DRM_PLANE_TYPE_PRIMARY &&
 	    plane_cap &&
 	    (plane_cap->pixel_format_support.nv12 ||