ARM: tegra: add missing clock documentation to DT bindings

Many of the Tegra DT binding documents say nothing about the clocks or
clock-names properties, yet those are present and required in DT files.
This patch simply updates the documentation file to match the implicit
definition of the binding, based on real-world DT content.

All Tegra bindings that mention clocks are updated to have consistent
wording and formatting of the clock-related properties.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-By: Terje Bergstrom <tbergstrom@nvidia.com>

Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt

@@ -7,6 +7,8 @@ Required properties:
 - reg: physical base address and length of the controller's registers
 - #pwm-cells: should be 2. See pwm.txt in this directory for a description of
   the cells format.
+- clocks: Must contain one entry, for the module clock.
+  See ../clocks/clock-bindings.txt for details.
 
 Example:
 
@@ -14,4 +16,5 @@ Example:
 		compatible = "nvidia,tegra20-pwm";
 		reg = <0x7000a000 0x100>;
 		#pwm-cells = <2>;
+		clocks = <&tegra_car 17>;
 	};