net: phy: Threaded interrupts allow some simplification

The PHY interrupts are now handled in a threaded interrupt handler,
which can sleep. The work queue is no longer needed, phy_change() can
be called directly. phy_mac_interrupt() still needs to be safe to call
in interrupt context, so keep the work queue, and use a helper to call
phy_change().

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>