MFC 264990, 264994, 265020, 265025:

MFC 264990, 264994, 265020, 265025:

  Call cpu_icache_sync_range() rather than sync_all since we know the range
  and flushing the entire icache is needlessly expensive.

  Provide a proper armv7 implementation of icache_sync_all rather than
  using armv7_idcache_wbinv_all, because wbinv_all doesn't broadcast the
  operation to other cores.  In elf_cpu_load_file() use icache_sync_all()
  and explain why it's needed (and why other sync operations aren't).

  Remove cpu_idcache_wbinv_all() from kdb_cpu_trap(), it's no longer needed.

  Explain why wbinv_all is SMP-safe when dumping, and add a missing l2 cache
  flush.  (Either it was missing here, or it isn't needed in the minidump
  case.  Adding it here seems like the safer path to consistancy.)

git-svn-id: svn://svn.freebsd.org/base/stable/10@266373 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f