net: mvpp2: fix validate for PPv2.1

[ Upstream commit 8b318f30ab4ef9bbc1241e6f8c1db366dbd347f2 ]

The Phylink validate function is the Marvell PPv2 driver makes a check
on the GoP id. This is valid an has to be done when using PPv2.2 engines
but makes no sense when using PPv2.1. The check done when using an RGMII
interface makes sure the GoP id is not 0, but this breaks PPv2.1. Fixes
it.

Fixes: 0fb628f0f250 ("net: mvpp2: fix phylink handling of invalid PHY modes")
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>