Make device_quiet() an attachment property.

In particular, reset the DF_QUIET flag when detaching from a device so
that a driver that marks a device quiet doesn't dictate policy for a
different driver that may claim the device in the future.

Reviewed by: rpokala, wblock
MFC after: 2 weeks
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D7803