net: phy: Add helper for fixing RGMII PHY mode based on internal mac delay

net: phy: Add helper for fixing RGMII PHY mode based on internal mac delay

The "phy-mode" property of devicetree indicates whether the PCB has
delay now, which means the mac needs to modify the PHY mode based
on whether there is an internal delay in the mac.

This modification is similar for many ethernet drivers. To simplify
code, define the helper phy_fix_phy_mode_for_mac_delays(speed, mac_txid,
mac_rxid) to fix PHY mode based on whether mac adds internal delay.

Suggested-by: Russell King (Oracle) <linux@armlinux.org.uk>
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251114003805.494387-3-inochiama@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>