Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC 239512:
Add a BUS_CHILD_DELETED() method that a bus can hook to allow it to cleanup
any bus-specific state (such as ivars) when a child device is deleted.

Add a BUS_CHILD_DELETED() method that a bus can hook to allow it to cleanup
any bus-specific state (such as ivars) when a child device is deleted.

Requested by: kan
MFC after: 1 month