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 r236997:
Add ARM callchain support for hwpmc.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Intel XScale hwpmc(4) support.

This brings hwpmc(4) support for 2nd and 3rd generation XScale cores.
Right now it's enabled by default to make sure we test this a bit.
When the time comes it can be disabled by default.
Tested on Gateworks boards.

A man page is coming.

Obtained from: //depot/user/rpaulo/xscalepmc/...

Add stubs to unbreak LINT.

MFP4:

- Implement sampling modes and logging support in hwpmc(4).

- Separate MI and MD parts of hwpmc(4) and allow sharing of
PMC implementations across different architectures.
Add support for P4 (EMT64) style PMCs to the amd64 code.

- New pmcstat(8) options: -E (exit time counts) -W (counts
every context switch), -R (print log file).

- pmc(3) API changes, improve our ability to keep ABI compatibility
in the future. Add more 'alias' names for commonly used events.

- bug fixes & documentation.

Add empty header (except of the multiple-inclusion protection) to
get hwpmc(4) to compile on this platform.