net: phy: Add phy_ignore_ta_mask to account for broken turn-around

Some PHY devices/switches will not release the turn-around line as they
should do at the end of a MDIO transaction. To help with such
situations, allow MDIO bus drivers to be made aware of such
restrictions.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>