Run mvs SATA driver on Armada XP instead of old mv_sata

The mvs driver seems to be more functional than mv_sata and is not
causing random interrupt storms during boot.
Include necessary headers that now are available due to pollution
via if_var.h.

Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
Instead of putting ifnet declaration into eventhandler.h, move
bpf(4) and vlan(4) related event declarations to bpf.h and
if_vlan_var.h. To avoid dependency on eventhandler.h, protect
these declarations with ifdef SYS_EVENTHANDLER_H.

Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.