dt-bindings: rtc: sun6i-rtc: Deprecate external clock output for A31

The A31 does not have an external clock output directly from the RTC.
Instead, it has four muxable clock outputs: three (A, B, C) are
controlled from the CCU, and the last (D) is controlled from the PRCM.

Deprecate the usage of the external clock output for the A31 compatible.
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/sun6i-rtc.txt

@@ -24,12 +24,14 @@ Required properties:
 
 Required properties for new device trees
 - clocks	: phandle to the 32kHz external oscillator
-- clock-output-names : names of the two clock outputs. See below.
+- clock-output-names : names of up to two clock outputs. See below.
 - #clock-cells  : must be equal to 1.
 
 The RTC provides the following clocks at the given indices:
 - 0: LOSC
 - 1: LOSC external output, known as X32KFOUT in the datasheet.
+     This clock is not available on the A31 and is deprecated for old
+     device trees still using the "allwinner,sun6i-a31-rtc" compatible.
 
 Example:
 
@@ -37,7 +39,7 @@ rtc: rtc@1f00000 {
 	compatible = "allwinner,sun6i-a31-rtc";
 	reg = <0x01f00000 0x54>;
 	interrupts = <0 40 4>, <0 41 4>;
-	clock-output-names = "osc32k", "osc32k-out";
+	clock-output-names = "osc32k";
 	clocks = <&ext_osc32k>;
 	#clock-cells = <1>;
 };