net: phy: Add BIT macro for Motorcomm yt8521/yt8531 gigabit ethernet phy

Add BIT macro for Motorcomm yt8521/yt8531 gigabit ethernet phy.
 This is a preparatory patch. Add BIT macro for 0xA012 reg, and
 supplement for 0xA001 and 0xA003 reg. These will be used to support dts.

Signed-off-by: Frank Sae <Frank.Sae@motor-comm.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>