net: phy: let genphy_c45_read_link manage the devices to check

Let genphy_c45_read_link manage the devices to check, this removes
overhead from callers. Add C22EXT to the list of excluded devices
because it doesn't implement the status register. According to the
802.3 clause 45 spec registers 29.0 - 29.4 are reserved.

At the moment we have very few clause 45 PHY drivers, so we are
lacking experience whether other drivers will have to exclude further
devices, or may need to check PHY XS. If we should figure out that
list of devices to check needs to be configurable, I think best will
be to add a device list member to struct phy_driver.

v2:
- adjusted commit message
- exclude also device C22EXT from link checking

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