iichid(4): Do not power down opened device in attach handler

Some iichid(4) child devices, currently hkbd(4) only, opens parent
device in their attach handlers. That breaks internal iichid(4) state
leading to rejecting any incoming data on software and hardware levels.

Fix it with adding of extra state check in iichid(4) attach handler.

Reported by: many
Submitted by: trasz (initial version)
PR: 280290
MFC after: 3 days