85xx: Additional fixes and cleanup of MP code

* adjust __spin_table alignment to match ePAPR v0.94 spec
* loop over all cpus when determing who is up.  This fixes an issue if
  the "boot cpu" isn't core0.  The "boot cpu" will already be in the
  cpu_up_mask so there is no harm
* Added some protection in the code to ensure proper behavior.  These
  changes are explicitly needed but don't hurt:
  - Added eieio to ensure the "hot word" of the table is written after
    all other table updates have occurred.
  - Added isync to ensure we don't prefetch loading of table entries
    until we a released

These issues we raised by Dave Liu.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>