log: Add some diagnostics to the log

Just a few useful things to get this started: egl vendor and extensions,
gles2 extensions, drm and kms info and just a bit of x11 backend info.
diff --git a/src/compositor-x11.c b/src/compositor-x11.c
index 4230a56..44a48b0 100644
--- a/src/compositor-x11.c
+++ b/src/compositor-x11.c
@@ -523,6 +523,9 @@
 
 	wl_list_insert(c->base.output_list.prev, &output->base.link);
 
+	weston_log("x11 output %dx%d, window id %d\n",
+		   width, height, output->window);
+
 	return 0;
 }
 
@@ -865,6 +868,8 @@
 	xcb_screen_iterator_t s;
 	int i, x;
 
+	weston_log("initializing x11 backend\n");
+
 	c = malloc(sizeof *c);
 	if (c == NULL)
 		return NULL;