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 r241745,241738,241741

Update hwpmc to support the Xeon class of Sandybridge processors.
(Model 0x2D /* Per Intel document 253669-044US 08/2012. */)

Update man page crossreferences to sandybridge xeon class

Remove trailing whitespace.

MFC r233628, r234598, r235229, r235831, r226986.

Add software PMC support.

New kernel events can be added at various location for sampling or counting.
This will for example allow easy system profiling whatever the processor is
with known tools like pmcstat(8).

Simultaneous usage of software PMC and hardware PMC is possible, for example
looking at the lock acquire failure, page fault while sampling on
instructions.

Sponsored by: NETASQ

MFC: r232366

- Add support for the Intel Sandy Bridge microarchitecture (both core and
uncore counting events)
- New manpages with event lists.
- Add MSRs for the Intel Sandy Bridge microarchitecture

Approved by: gnn (mentor)

- Add support for the Intel Sandy Bridge microarchitecture (both core and uncore counting events)
- New manpages with event lists.
- Add MSRs for the Intel Sandy Bridge microarchitecture

Reviewed by: attilio, brueffer, fabient
Approved by: gnn (mentor)
MFC after: 3 weeks