compositor-drm: Force DPMS state to ON after drmModeSetCrtc()

The kernel is supposed to set this when drmModeSetCrtc() is called but
at least the i915 driver wouldn't do that in all cases. A fix for this
should be released with kernel 3.10, but we work around the issue in
older kernels by always forcing DPMS to ON when doing a mode set.

https://bugs.freedesktop.org/show_bug.cgi?id=64873

src/compositor-drm.c

@@ -588,6 +588,7 @@ drm_output_repaint(struct weston_output *output_base,
 			weston_log("set mode failed: %m\n");
 			return;
 		}
+		output_base->set_dpms(output_base, WESTON_DPMS_ON);
 	}
 
 	if (drmModePageFlip(compositor->drm.fd, output->crtc_id,