net: ngbe: Add ngbe mdio bus driver.

Add mdio bus register for ngbe.
The internal phy and external phy need to be handled separately.
Add phy changed event detection.

Signed-off-by: Mengyuan Lou <mengyuanlou@net-swift.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230111111718.40745-1-mengyuanlou@net-swift.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>