net: phy: Add Airoha phy library for shared code

net: phy: Add Airoha phy library for shared code

In preparation of Airoha AN8801R PHY support, split out the interface
functions that will be common between the already present air_en8811h
driver and the new one, and put them into a new library named
air_phy_lib.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
Link: https://patch.msgid.link/20260526-add-airoha-an8801-support-v5-2-01aea8dee69b@collabora.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>