net: ethernet: aquantia: Common functions and definitions

Add files containing the functions and definitions used in common in
different functional areas.

Signed-off-by: Alexander Loktionov <Alexander.Loktionov@aquantia.com>
Signed-off-by: Dmitrii Tarakanov <Dmitrii.Tarakanov@aquantia.com>
Signed-off-by: Pavel Belous <Pavel.Belous@aquantia.com>
Signed-off-by: Dmitry Bezrukov <Dmitry.Bezrukov@aquantia.com>
Signed-off-by: David M. VomLehn <vomlehn@texas.net>
Signed-off-by: David S. Miller <davem@davemloft.net>