ARM: dts: am335x-chiliboard: add /chosen/tick-timer

Commit 4b2be78ab6 ("time: Fix get_ticks being non-monotonic") has
broken boot on chiliboard platform, as it requires '/chosen/tick-timer'
in device-tree. This resulted in following panic message:

  Could not initialize timer (err -19)

Provide missing chosen property in device-tree to fix chiliboard
support.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>

arch/arm/dts/am335x-chiliboard-u-boot.dtsi

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0+ or X11
 /*
- * Copyright (C) 2018 Grinn Sp. z o.o. -- http://www.grinn-global.com/
+ * Copyright (C) 2018-2021 Grinn Sp. z o.o. -- http://www.grinn-global.com/
  * Author: Marcin Niestroj <m.niestroj@grinn-global.com>
  */
 
@@ -9,5 +9,6 @@
 / {
 	chosen {
 		stdout-path = &uart0;
+		tick-timer = &timer2;
 	};
 };