mm/pkeys, powerpc, x86: Provide an empty vma_pkey() in linux/pkeys.h

Consolidate the pkey handling by providing a common empty definition
of vma_pkey() in pkeys.h when CONFIG_ARCH_HAS_PKEYS=n.

This also removes another entanglement of pkeys.h and
asm/mmu_context.h.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Ram Pai <linuxram@us.ibm.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>

arch/powerpc/include/asm/mmu_context.h

@@ -250,11 +250,6 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 #define thread_pkey_regs_restore(new_thread, old_thread)
 #define thread_pkey_regs_init(thread)
 
-static inline int vma_pkey(struct vm_area_struct *vma)
-{
-	return 0;
-}
-
 static inline u64 pte_to_hpte_pkey_bits(u64 pteflags)
 {
 	return 0x0UL;

arch/x86/include/asm/mmu_context.h

@@ -296,11 +296,6 @@ static inline int vma_pkey(struct vm_area_struct *vma)
 
 	return (vma->vm_flags & vma_pkey_mask) >> VM_PKEY_SHIFT;
 }
-#else
-static inline int vma_pkey(struct vm_area_struct *vma)
-{
-	return 0;
-}
 #endif
 
 /*

include/linux/pkeys.h

@@ -13,6 +13,11 @@
 #define PKEY_DEDICATED_EXECUTE_ONLY 0
 #define ARCH_VM_PKEY_FLAGS 0
 
+static inline int vma_pkey(struct vm_area_struct *vma)
+{
+	return 0;
+}
+
 static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 {
 	return (pkey == 0);