dt-bindings: phy: bcm-ns-usb2-phy: convert to yaml

1. Convert from txt to yaml
2. Drop "Driver for" from the title
3. Document "#phy-cells"
4. Fix example node name (noticed by dt_binding_check)
5. Add #include to example (noticed by dt_binding_check)
6. Specify license

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210329165041.31574-1-zajec5@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>