staging: dt-bindings: wilc1000: add optional rtc_clk property

Add bindings for optional rtc clock pin.
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Ajay Singh <ajay.kathat@microchip.com>
Link: https://lore.kernel.org/r/1568037993-4646-1-git-send-email-eugen.hristev@microchip.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/microchip,wilc1000,sdio.txt

@@ -10,7 +10,9 @@ Required properties:
 
 Optional:
 - bus-width	:	Number of data lines wired up the slot. Default 1 bit.
-
+- rtc_clk	:	Clock connected on the rtc clock line. Must be assigned
+			a frequency with assigned-clocks property, and must be
+			connected to a clock provider.
 
 Examples:
 mmc1: mmc@fc000000 {
@@ -24,6 +26,10 @@ mmc1: mmc@fc000000 {
 		wilc_sdio@0 {
 			compatible = "microchip,wilc1000-sdio";
 			irq-gpios = <&pioC 27 0>;
+			clocks = <&pck1>;
+			clock-names = "rtc_clk";
+			assigned-clocks = <&pck1>;
+			assigned-clock-rates = <32768>;
 			status = "okay";
 			reg = <0>;
 			bus-width = <4>;

drivers/staging/wilc1000/microchip,wilc1000,spi.txt

@@ -9,6 +9,10 @@ Required properties:
 - reg			: Chip select address of device
 - irq-gpios		: Connect to a host IRQ
 
+Optional:
+- rtc_clk	:	Clock connected on the rtc clock line. Must be assigned
+			a frequency with assigned-clocks property, and must be
+			connected to a clock provider.
 
 Examples:
 
@@ -21,6 +25,10 @@ spi1: spi@fc018000 {
 			spi-max-frequency = <48000000>;
 			reg = <0>;
 			irq-gpios = <&pioC 27 0>;
+			clocks = <&pck1>;
+			clock-names = "rtc_clk";
+			assigned-clocks = <&pck1>;
+			assigned-clock-rates = <32768>;
 			status = "okay";
 		};
 };