net: phy: add support for clause 37 auto-negotiation

This patch adds support for clause 37 1000Base-X auto-negotiation.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Tao Ren <taoren@fb.com>
Tested-by: René van Dorst <opensource@vdorst.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>