MFC r340387: Add evdev support to amd64 and i386

This merge is done sans sys/i386/conf/MINIMAL, since that doesn't exist in
stable/12, only current.

Include evdev support and drivers in the amd64 GENERIC and MINIMAL, and i386
GENERIC 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