dt-bindings: clk: meson: add g12b periph clock controller bindings

Update the documentation to support clock driver for the Amlogic G12B SoC.

G12B clock driver is very close, the main differences are :
- the clock tree is duplicated for the both clusters, and the
  SYS_PLL are swapped between the clusters
- G12B has additional clocks like for CSI an other components

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>

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

@@ -10,6 +10,7 @@ Required Properties:
 		"amlogic,gxl-clkc" for GXL and GXM SoC,
 		"amlogic,axg-clkc" for AXG SoC.
 		"amlogic,g12a-clkc" for G12A SoC.
+		"amlogic,g12b-clkc" for G12B SoC.
 - clocks : list of clock phandle, one for each entry clock-names.
 - clock-names : should contain the following:
   * "xtal": the platform xtal