[evdev] Add evdev support to kbdmux(4) driver

To enable event sourcing from kbdmux(4) kern.evdev.rcpt_mask value
should have bit 1 set (this is default)

Submitted by: Vladimir Kondratiev <wulf@cicgroup.ru>
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D8437