net: stmmac: add stmmac_get_phy_intf_sel()

net: stmmac: add stmmac_get_phy_intf_sel()

Provide a function to translate the PHY interface mode to the
phy_intf_sel pin configuration for dwmac1000 and dwmac4 cores that
support multiple interfaces. We currently handle MII, GMII, RGMII,
SGMII, RMII and REVMII, but not TBI, RTBI nor SMII as drivers do not
appear to use these three and the driver doesn't currently support
these.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vFt4c-0000000Choe-3SII@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>