MFC elfdump improvements

r269092: Improve section type reporting

  The SHT range 0x70000000-0x7fffffff is processor-specific.  Pass the
  ELF machine type header to sh_types so the section header type name can
  be reported correctly for the given processor.

  For all ranges report the actual value for unknown types.

  Add MIPS-specific type SHT_MIPS_OPTIONS.

r269143 (andreast): Further improvements on elfdump, to follow up r269092:

  - Add ARM specific section header types.
  - Add SHT_GNU_HASH section header type.
  - Improve reporting of undefined tags in d_tags.
  - Add DT_GNU_HASH tag.

  Reviewed by:	emaste

r269337: add EM_AARCH64 64-bit ARM machine architecture

r269338: use existing ELF constants where available

r270303: Rename DT_FEATURE_1 to DT_FEATURE

  This provides a minor cleanup in elfdump; there are otherwise no
  consumers in the tree.  Old SUN documentation can be found for either
  variant, but GNU binutils switched to DT_FEATURE around 2000.

r270304: Remove extraneous _SUNW_ in reported DT_ names

Sponsored by:	The FreeBSD Foundation