kernel: alx driver for AR816x/AR817x Ethernet

kernel: alx driver for AR816x/AR817x Ethernet

These ethernet cards can be found onboard various x86 and
x86_64 Gigabyte mainboards since the sandy-bridge/ ivy-bridge era.

This driver supports the following QCA/"Killer" ethernet cards:

	1969:1091 - AR8161 Gigabit Ethernet
	1969:1090 - AR8162 Fast Ethernet
	1969:10A1 - AR8171 Gigabit Ethernet
	1969:10A0 - AR8172 Fast Ethernet

	1969:E091 - Killer E2200 Gigabit Ethernet
	1969:E0A1 - Killer E2400 Gigabit Ethernet
	1969:E0B1 - Killer E2500 Gigabit Ethernet

Successfully runtime tested with the onboard ethernet card of a
Gigabyte GA-H77M-D3H ivy-bridge mainboard (x86_64/EFI image):

02:00.0 Ethernet controller [0200]: Qualcomm Atheros AR8161 [...]
	Subsystem: Gigabyte Technology Co., Ltd AR8161 [...]
	Kernel driver in use: alx
	Kernel modules: alx

alx 0000:02:00.0 eth0: Qualcomm Atheros AR816x/AR817x Ethernet [...]
alx 0000:02:00.0 eth0: NIC Up: 1 Gbps Full

Signed-off-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com> [fix typo,
shorten subject to <50 characters, shorten lines to <76 chars.]