mm/vmacache, sched/headers: Introduce 'struct vmacache' and move it from <linux/sched.h> to <linux/mm_types>

The <linux/sched.h> header includes various vmacache related defines,
which are arguably misplaced.

Move them to mm_types.h and minimize the sched.h impact by putting
all task vmacache state into a new 'struct vmacache' structure.

No change in functionality.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/mm/nommu.c b/mm/nommu.c
index fe9f4fa..aae06e8 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -757,7 +757,7 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
 	mm->map_count--;
 	for (i = 0; i < VMACACHE_SIZE; i++) {
 		/* if the vma is cached, invalidate the entire cache */
-		if (curr->vmacache[i] == vma) {
+		if (curr->vmacache.vmas[i] == vma) {
 			vmacache_invalidate(mm);
 			break;
 		}