dt-bindings: net: convert Broadcom Starfighter 2 binding to the json-schema

This helps validating DTS files. Only the current (not deprecated one)
binding was converted.

Minor changes:
1. Dropped dsa/dsa.txt references
2. Updated node name to match dsa.yaml requirement
3. Fixed 2 typos in examples

The new binding was validated using the dt_binding_check.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Link: https://lore.kernel.org/r/20210106213202.17459-1-zajec5@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>