mm/vma: make vma_is_foreign() available for general use

Idea of a foreign VMA with respect to the present context is very generic.
But currently there are two identical definitions for this in powerpc and
x86 platforms.  Lets consolidate those redundant definitions while making
vma_is_foreign() available for general use later.  This should not cause
any functional change.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Link: http://lkml.kernel.org/r/1582782965-3274-3-git-send-email-anshuman.khandual@arm.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/include/asm/mmu_context.h

@@ -213,21 +213,6 @@ static inline void arch_unmap(struct mm_struct *mm, unsigned long start,
  * So do not enforce things if the VMA is not from the current
  * mm, or if we are in a kernel thread.
  */
-static inline bool vma_is_foreign(struct vm_area_struct *vma)
-{
-	if (!current->mm)
-		return true;
-	/*
-	 * Should PKRU be enforced on the access to this VMA?  If
-	 * the VMA is from another process, then PKRU has no
-	 * relevance and should not be enforced.
-	 */
-	if (current->mm != vma->vm_mm)
-		return true;
-
-	return false;
-}
-
 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 		bool write, bool execute, bool foreign)
 {