Allow RandR get output property to call into drivers

In order to report accurate values to users of the RandR property interface,
it's sometimes necessary to ask the driver to update the value (for example
when backlight brightness changes without the server's knowledge, due to hotkey
events or direct sysfs banging).

This patch wires up the core server code with a new xf86CrtcFuncs callback,
get_property, to allow for this.

The new code is available under the RANDR_13_INTERFACE define, which in turn
depends on the RANDR_12_INTERFACE code.

randr/mirandr.c

@@ -73,6 +73,14 @@ miRROutputSetProperty (ScreenPtr	    pScreen,
     return TRUE;
 }
 
+Bool
+miRROutputGetProperty (ScreenPtr	    pScreen,
+		       RROutputPtr	    output,
+		       Atom		    property)
+{
+	return TRUE;
+}
+
 Bool
 miRROutputValidateMode (ScreenPtr	    pScreen,
 			RROutputPtr	    output,
@@ -116,6 +124,9 @@ miRandRInit (ScreenPtr pScreen)
     pScrPriv->rrCrtcSet = miRRCrtcSet;
     pScrPriv->rrCrtcSetGamma = miRRCrtcSetGamma;
     pScrPriv->rrOutputSetProperty = miRROutputSetProperty;
+#if RANDR_13_INTERFACE
+    pScrPriv->rrOutputGetProperty = miRROutputGetProperty;
+#endif
     pScrPriv->rrOutputValidateMode = miRROutputValidateMode;
     pScrPriv->rrModeDestroy = miRRModeDestroy;