Siteinfo cleanup

Siteinfo cleanup

- 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
- Instead of specifically looking for '${FILE_DIRNAME}/site-${PV}/<sitefile>',
  leverage FILESPATH.  Now it searches the paths in both BBPATH and FILESPATH
  for "site/<sitefile>".
- SITEINFO_ENDIANESS -> SITEINFO_ENDIANNESS

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