clk: shmobile: document DIV6 clock parent bindings

Describes how to specify the parents for clocks with EXSRC bits.

Signed-off-by: Ulrich Hecht <[e-mail]>
Signed-off-by: Geert Uytterhoeven <[e-mail]>

Documentation/devicetree/bindings/clock/renesas,cpg-div6-clocks.txt

···
 Required Properties:
 
   - compatible: Must be one of the following
+    - "renesas,r8a73a4-div6-clock" for R8A73A4 (R-Mobile APE6) DIV6 clocks
+    - "renesas,r8a7740-div6-clock" for R8A7740 (R-Mobile A1) DIV6 clocks
     - "renesas,r8a7790-div6-clock" for R8A7790 (R-Car H2) DIV6 clocks
     - "renesas,r8a7791-div6-clock" for R8A7791 (R-Car M2) DIV6 clocks
+    - "renesas,sh73a0-div6-clock" for SH73A0 (SH-Mobile AG5) DIV6 clocks
     - "renesas,cpg-div6-clock" for generic DIV6 clocks
   - reg: Base address and length of the memory resource used by the DIV6 clock
-  - clocks: Reference to the parent clock
+  - clocks: Reference to the parent clock(s); either one, four, or eight
+    clocks must be specified.  For clocks with multiple parents, invalid
+    settings must be specified as "<0>".
   - #clock-cells: Must be 0
   - clock-output-names: The name of the clock as a free-form string
 
···
 Example
 -------
 
-	sd2_clk: sd2_clk@e6150078 {
-		compatible = "renesas,r8a7790-div6-clock", "renesas,cpg-div6-clock";
-		reg = <0 0xe6150078 0 4>;
-		clocks = <&pll1_div2_clk>;
+	sdhi2_clk: sdhi2_clk@e615007c {
+		compatible = "renesas,r8a73a4-div6-clock", "renesas,cpg-div6-clock";
+		reg = <0 0xe615007c 0 4>;
+		clocks = <&pll1_div2_clk>, <&cpg_clocks R8A73A4_CLK_PLL2S>,
+			 <0>, <&extal2_clk>;
 		#clock-cells = <0>;
-		clock-output-names = "sd2";
+		clock-output-names = "sdhi2ck";
 	};