Siteinfo cleanup v2

Siteinfo cleanup v2

- Don't supply site files for native.
- Split up the site information, so we don't need to add every single
  combination of os and architecture to the siteinfo.bbclass.
- Drop the ${FILE_DIRNAME}/site-<bits> stuff, there are other ways to do it.
- SITEINFO_ENDIANESS -> SITEINFO_ENDIANNESS.

Signed-off-by: Chris Larson <clarson@kergoth.com>