net: phy: add register modifying helpers returning 1 on change

When modifying registers there are scenarios where we need to know
whether the register content actually changed. This patch adds
new helpers to not break users of the current ones, phy_modify() etc.

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