bhnd(4): Fix resource allocation issues exposed by chipc PMU support.

• Delete all chipc children on attachment failure.
• Added missing bhnd_nexus bhnd_bus_deactivate_resource implementation.
• Drop a CHIPC_UNLOCK() accidentally left behind after lifting synchronization into the chipc region refcounting API.
• Fix re-allocation of chipc resources. Previously, the resource ID was reset to -1 on release, preventing later re-allocation.

Approved by: re (gjb), adrian (mentor)
Differential Revision: https://reviews.freebsd.org/D6849