Patches to support SMP.

* Each CPU has its own current_pgd.
* flush_tlb_range is implemented as flush_tlb_mm.
* Atomic operations implemented with spinlocks.
* Semaphores implemented with spinlocks.

Signed-off-by: Mikael Starvik
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds