net: wangxun: move MDIO bus implementation to the library

Move similar code of accessing MDIO bus from txgbe/ngbe to libwx.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230912031424.721386-1-jiawenwu@trustnetic.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>