backend-headless: support all EOTF modes

The headless backend does not display to anything, so it doesn't care
what the EOTF mode is. To allow testing compositor internal behavior,
claim to support all EOTF modes.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/backend-headless/headless.c

@@ -361,6 +361,8 @@ headless_head_create(struct weston_compositor *compositor,
 
 	weston_head_init(&head->base, name);
 	weston_head_set_connection_status(&head->base, true);
+	weston_head_set_supported_eotf_mask(&head->base,
+					    WESTON_EOTF_MODE_ALL_MASK);
 
 	/* Ideally all attributes of the head would be set here, so that the
 	 * user has all the information when deciding to create outputs.