Add evdev support to amd64 and i386 kernels

Include evdev support and drivers in the amd64 and i386 GENERIC and MINIMAL
kernels. Evdev is used by X and wayland to handle input devices, and this
change, together with upcomming changes in ports will make us handle input
devices better in graphical UIs.

Reviewed by: wulf, bapt, imp
Approved by: imp
Differential Revision: https://reviews.freebsd.org/D17912