net: phy: aquantia: move priv and hw stat to header

In preparation for LEDs support, move priv and hw stat to header to
reference priv struct also in other .c outside aquantia.main

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>