[ARM SMP] Do not clear cpu_vm_mask for VIPT caches

Since we do not invalidate TLBs/caches on MM switches, we should not
clear the cpu_vm_mask for the CPU.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/mmu_context.h

@@ -86,7 +86,8 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 		cpu_set(cpu, next->cpu_vm_mask);
 		check_context(next);
 		cpu_switch_mm(next->pgd, next);
-		cpu_clear(cpu, prev->cpu_vm_mask);
+		if (cache_is_vivt())
+			cpu_clear(cpu, prev->cpu_vm_mask);
 	}
 }