net: phy: mxl-86110: add basic support for MxL86111 PHY

net: phy: mxl-86110: add basic support for MxL86111 PHY

Add basic support for the MxL86111 PHY which in addition to the features
of the MxL86110 also comes with an SGMII interface.
Setup the interface mode and take care of in-band-an.

Currently only RGMII-to-UTP and SGMII-to-UTP modes are supported while the
PHY would also support RGMII-to-1000Base-X, including automatic selection
of the Fiber or UTP link depending on the presence of a link partner.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/707fd83ec0e11ea620d37f2125a394e9dd1b27fa.1755884175.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>