MFC: r203833

MFC: r203833

- At least the trap table of the Sun Fire V1280 firmware apparently has
  no cleanwindows handler so just remove trying to trigger it from _start
  and the AP trampoline code as that leads to a crash there. This should
  be okay as leaking data from the OFW via the CPU registers on start of
  the kernel should be no real concern.
- Make the comments of _start and the AP trampoline code regarding the
  initializations they perform match each other and reality.
- Make the comments of the AP trampoline code regarding iTLB accesses
  refer to the right macro.

git-svn-id: svn://svn.freebsd.org/base/stable/8@205924 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f