net: phy: switch drivers to use dynamic feature detection

Recently genphy_read_abilities() has been added that dynamically detects
clause 22 PHY abilities. I *think* this detection should work with all
supported PHY's, at least for the ones with basic features sets, i.e.
PHY_BASIC_FEATURES and PHY_GBIT_FEATURES. So let's remove setting these
features explicitly and rely on phylib feature detection.

I don't have access to most of these PHY's, therefore I'd appreciate
regression testing.

v2:
- make the feature constant a comment so that readers know which
  features are supported by the respective PHY

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>