Unfortunately the restoring of SPE state was causing data corruption
since we were restoring based on the size of the altivec context and not
the SPE context.  Also, fixed setting of last_task_used_spe on
start_thread, flush_thread, and exit_thread. 
Signed-off-by: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>