Document r266890, pmcstat(8) '-l' flag.

Sponsored by:	The FreeBSD Foundation
MFC r267326, r267327:

r267326:
  Add empty pkg-stage file to CLEANFILES if WITH_DVD=1.

r267327:
  Fix indentation level.

Sponsored by:	The FreeBSD Foundation
MFC 266263,266551,266552:
- Add definitions for more structured extended features as well as
  XSAVE Extended Features for AVX512 and MPX (Memory Protection Extensions).
- Don't permit users to request a subset of the AVX512 or MPX xsave masks.
Fix a typo in note for r266890, pmcstat(8)

Sponsored by:	The FreeBSD Foundation