Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

- Add the 'cmp' and 'core' pseudo-busses which are used to group CPU cores
to the exclusion lists as the CPU nodes aren't handled as regular devices
either. Also add the pseudo-devices found in Sun Fire V1280.
- Allow nexus_attach() and nexus_alloc_resource() to be used by drivers
derived from nexus(4) for subordinate busses.
- Don't add the zero-sized memory resources of glue devices to the resource
lists.

Resurrect nexusvar.h from r167307.

Some cleanups to the nexus code:
- Remove second license, the first was not that different and should be
fine.
- Add nexus_attach(), and do not perform its task in nexus_probe() any
more.
- Remove nexus_write_ivar(), since it was quite pointless.
- Remove superfluous devinfo members.
- Clean up some comments, minor style issues and prototypes.

Correct the defintion of struct ofw_upa_regs, and use it instead of
struct ofw_nexus_reg. Implement UPA device memory management in the
nexus driver.
Adapt the psycho driver to these changes, and do some minor cleanup work
while being there.

Add a nexus device for sparc64, which uses the OpenFirmware to attach UPA
devices (mostly host bridges) and handles interrupt allocation and setup.