net: phy: add constants for fast retrain related register

Add the constants for 2.5G fast retrain capability
in 10G AN control register, fast retrain status and
control register and THP bypass register into mdio.h.

Signed-off-by: Luo Jie <luoj@codeaurora.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>