dt-bindings: net: Add compatible for AM64x in ICSSG

Add compatible for AM64x in icssg-prueth dt bindings. AM64x supports
ICSSG similar to AM65x SR2.0.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>