backend/drm: add support for atomic tearing page-flips

The kernel patches [1] have been merged.

[1]: https://patchwork.freedesktop.org/series/120103/

backend/drm/drm.c

@@ -114,6 +114,8 @@ bool check_drm_features(struct wlr_drm_backend *drm) {
 
 	if (drm->iface == &legacy_iface) {
 		drm->supports_tearing_page_flips = drmGetCap(drm->fd, DRM_CAP_ASYNC_PAGE_FLIP, &cap) == 0 && cap == 1;
+	} else {
+		drm->supports_tearing_page_flips = drmGetCap(drm->fd, DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP, &cap) == 0 && cap == 1;
 	}
 
 	if (env_parse_bool("WLR_DRM_NO_MODIFIERS")) {

meson.build

@@ -109,7 +109,7 @@ wayland_server = dependency('wayland-server',
 )
 
 drm = dependency('libdrm',
-	version: '>=2.4.118',
+	version: '>=2.4.120',
 	fallback: 'libdrm',
 	default_options: [
 		'intel=disabled',