dt-bindings: net: sparx5: don't require a reset line

Make the reset line optional. It turns out, there is no dedicated reset
for the switch. Instead, the reset which was used up until now, was kind
of a global reset. This is now handled elsewhere, thus don't require a
reset.

Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>