evdev: Disable value normalization and state filtering for SND events.

Some events can take sound pitch as a value so can not be represented
as binary on/off events. Tracking for on/off state is left in place
as it is a part of the evdev API.

Reviewed by: gonzo
Approved by: gonzo (mentor)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D12676