net: stmmac: only call stmmac_pcs_ctrl_ane() for integrated SGMII PCS

net: stmmac: only call stmmac_pcs_ctrl_ane() for integrated SGMII PCS

The internal PCS registers only exist if the core is synthesized with
SGMII, TBI or RTBI support. They have no relevance for RGMII.

However, priv->hw->pcs contains a STMMAC_PCS_RGMII flag, which is set
if a PCS has been synthesized but we are operating in RGMII mode. As
the register has no effect for RGMII, there is no point calling
stmmac_pcs_ctrl_ane() in this case. Add a comment describing this
and make it conditional on STMMAC_PCS_SGMII.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/E1v9P6s-0000000AomE-2pAa@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>