dt-bindings: timer: Add X1000 bindings.

Add the timer bindings for the X1000 Soc from Ingenic.
Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1582100974-129559-3-git-send-email-zhouyanjie@wanyeetech.com

Documentation/devicetree/bindings/timer/ingenic,tcu.txt

@@ -10,6 +10,7 @@ Required properties:
   * ingenic,jz4740-tcu
   * ingenic,jz4725b-tcu
   * ingenic,jz4770-tcu
+  * ingenic,x1000-tcu
   followed by "simple-mfd".
 - reg: Should be the offset/length value corresponding to the TCU registers
 - clocks: List of phandle & clock specifiers for clocks external to the TCU.