net: usb: aqc111: Introduce PHY access

Add helpers to write 32bit values.
Implement PHY power up/down sequences.
AQC111, PHY is being controlled via vendor command interface.

Signed-off-by: Dmitry Bezrukov <dmitry.bezrukov@aquantia.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>