net: phy: provide whether link has changed in c37_read_status

Some PHY driver might require additional regs call after
genphy_c37_read_status() is called.

Expand genphy_c37_read_status to provide a bool wheather the link has
changed or not to permit PHY driver to skip additional regs call if
nothing has changed.

Every user of genphy_c37_read_status() is updated with the new
additional bool.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>