dt-bindings: clock: meson: update documentation with hhi syscon

The HHI register region hosts more than just clocks and needs to
accessed drivers other than the clock controller, such as the display
driver.

This register region should be managed by syscon. It is already the case
on gxbb/gxl and it soon will be on axg. The clock controllers must use
this system controller instead of directly mapping the registers.

This changes the bindings of gxbb and axg's clock controllers. This is
due to an initial 'incomplete' knowledge of these SoCs, which is why the
meson bindings are unstable ATM.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

Documentation/devicetree/bindings/clock/amlogic,gxbb-clkc.txt

@@ -10,9 +10,6 @@ Required Properties:
 		"amlogic,gxl-clkc" for GXL and GXM SoC,
 		"amlogic,axg-clkc" for AXG SoC.
 
-- reg: physical base address of the clock controller and length of memory
-       mapped region.
-
 - #clock-cells: should be 1.
 
 Each clock is assigned an identifier and client nodes can use this identifier
@@ -20,13 +17,22 @@ to specify the clock which they consume. All available clocks are defined as
 preprocessor macros in the dt-bindings/clock/gxbb-clkc.h header and can be
 used in device tree sources.
 
+Parent node should have the following properties :
+- compatible: "syscon", "simple-mfd, and "amlogic,meson-gx-hhi-sysctrl" or
+              "amlogic,meson-axg-hhi-sysctrl"
+- reg: base address and size of the HHI system control register space.
+
 Example: Clock controller node:
 
-	clkc: clock-controller@c883c000 {
+sysctrl: system-controller@0 {
+	compatible = "amlogic,meson-gx-hhi-sysctrl", "syscon", "simple-mfd";
+	reg = <0 0 0 0x400>;
+
+	clkc: clock-controller {
 		#clock-cells = <1>;
 		compatible = "amlogic,gxbb-clkc";
-		reg = <0x0 0xc883c000 0x0 0x3db>;
 	};
+};
 
 Example: UART controller node that consumes the clock generated by the clock
   controller: