net: phy: at803x: improve the WOL feature

The wol feature is controlled by the MMD3.8012 bit5,
need to set this bit when the wol function is enabled.

The reg18 bit0 is for enabling WOL interrupt, when wol
occurs, the wol interrupt status reg19 bit0 is set to 1.

Call phy_trigger_machine if there are any other interrupt
pending in the function set_wol.

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