bhnd(4): Implement common API for IOST/IOCTL register access and core reset
- Added bhnd(4) bus APIs for per-core ioctl/iost register access.
- Updated reset/suspend bhnd(4) APIs for compatibility with ioctl/iost changes.
- Implemented core reset/suspend support for both bcma(4) and siba(4).
- Implemented explicit release of all outstanding PMU requests at the bus level when putting a core into reset.
Approved by: adrian (mentor, implicit)
Differential Revision: https://reviews.freebsd.org/D8009