MIPS is interesting and has hardware variants that reorder over ll/sc
as well as those that do not.

Implement the 2 new barrier functions as per the old barriers.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-9ph49jbae3hol9v721sbc2g6@git.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maciej W. Rozycki" <macro@codesourcery.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>