MFC r315176-r315178

r315176:
[evdev] Do not ignore result evdev_register in UI_DEV_CREATE handler

Make sure that uinput state field reflects actual state by checking
evdev_register result for errors

Submitted by: Vladimir Kondratiev <wulf@cicgroup.ru>
Differential Revision: https://reviews.freebsd.org/D9320

r315177:
[evdev] Fix race condition between client's event queue reading and dropping

Submitted by: Vladimir Kondratiev <wulf@cicgroup.ru>
Differential Revision: https://reviews.freebsd.org/D9320

r315178:
[evdev] Fix Right Alt and Keypad Enter event codes for atkbd(4) and kbdmux(4) drivers

Submitted by: Vladimir Kondratiev <wulf@cicgroup.ru>
Differential Revision: https://reviews.freebsd.org/D9320