Felix Radensky noted that chip resets were generating stack trace dumps.
This is because the driver is attempting to acquire the mdio bus mutex
while holding the tp->lock spinlock.  The fix is to change the code such
that every phy access takes the tp->lock spinlock instead.
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>