dt-bindings: tegra: Update compatible strings for Tegra flowctrl

Update the compatible strings for Tegra Flow Control driver to match
the device-tree source files for Tegra.
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-flowctrl.txt

 NVIDIA Tegra Flow Controller
 
 Required properties:
-- compatible: Should be "nvidia,tegra<chip>-flowctrl"
+- compatible: Should contain one of the following:
+  - "nvidia,tegra20-flowctrl": for Tegra20
+  - "nvidia,tegra30-flowctrl": for Tegra30
+  - "nvidia,tegra114-flowctrl": for Tegra114
+  - "nvidia,tegra124-flowctrl": for Tegra124
+  - "nvidia,tegra132-flowctrl", "nvidia,tegra124-flowctrl": for Tegra132
+  - "nvidia,tegra210-flowctrl": for Tegra210
 - reg: Should contain one register range (address and length)
 
 Example: