dt-bindings: phy: bcm-ns-usb3-phy: convert to yaml

1. Change syntax from txt to yaml
2. Drop "Driver for" from the title
3. Drop "reg = <0x0>;" from example (noticed by dt_binding_check)
4. Specify license

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210329165056.31647-1-zajec5@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>