arm64: move update_mmu_cache() into asm/pgtable.h

Mark Brown reported an allnoconfig build failure in -next:

  Today's linux-next fails to build an arm64 allnoconfig due to "mm:
  make GUP handle pfn mapping unless FOLL_GET is requested" which
  causes:

  >       arm64-allnoconfig
  > ../mm/gup.c:51:4: error: implicit declaration of function
    'update_mmu_cache' [-Werror=implicit-function-declaration]

Fix the error by moving the function to asm/pgtable.h, as is the case
for most other architectures.
Reported-by: NMark Brown <broonie@kernel.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -505,6 +505,21 @@ extern int kern_addr_valid(unsigned long addr);
 
 #define pgtable_cache_init() do { } while (0)
 
+/*
+ * On AArch64, the cache coherency is handled via the set_pte_at() function.
+ */
+static inline void update_mmu_cache(struct vm_area_struct *vma,
+				    unsigned long addr, pte_t *ptep)
+{
+	/*
+	 * set_pte() does not have a DSB for user mappings, so make sure that
+	 * the page table write is visible.
+	 */
+	dsb(ishst);
+}
+
+#define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_PGTABLE_H */

arch/arm64/include/asm/tlbflush.h

@@ -154,20 +154,6 @@ static inline void __flush_tlb_pgtable(struct mm_struct *mm,
 	asm("tlbi	vae1is, %0" : : "r" (addr));
 	dsb(ish);
 }
-/*
- * On AArch64, the cache coherency is handled via the set_pte_at() function.
- */
-static inline void update_mmu_cache(struct vm_area_struct *vma,
-				    unsigned long addr, pte_t *ptep)
-{
-	/*
-	 * set_pte() does not have a DSB for user mappings, so make sure that
-	 * the page table write is visible.
-	 */
-	dsb(ishst);
-}
-
-#define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)
 
 #endif