net: stmmac: socfpga: Don't check for phy to enable the SGMII adapter

net: stmmac: socfpga: Don't check for phy to enable the SGMII adapter

The SGMII adapter needs to be enabled for both Cisco SGMII and 1000BaseX
operations. It doesn't make sense to check for an attached phydev here,
as we simply might not have any, in particular if we're using the
1000BaseX interface mode.

Make so that we only re-enable the SGMII adapter when it's present, and
when we use a phy_mode that is handled by said adapter.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20250424071223.221239-3-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>