David Brownell <david-b@pacbell.net> Clean up some Cortex-M3 reset handling.

 - AIRCR_SYSRESETREQ is generic; use it on any system where
  SRST won't fly, not just on Stellaris-based ones.

 - Reformat and improve comments about the Stellaris quirk; and
  xref the only public docs (an email) about the issue.

It seems that *most* Stellaris chips have this problem.  Tempest
parts aren't yet in general sampling; and if rev B silicon for
earlier chips exists, it's not very visible yet.

git-svn-id: svn://svn.berlios.de/openocd/trunk@2595 b42882b7-edfa-0310-969c-e2dbd0fdcd60