ARM: pgtable: provide get_top_pte() to complement set_top_pte()

Provide get_top_pte() to complement set_top_pte(), moving the only
users of TOP_PTE to arch/arm/mm/mm.h.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/highmem.c

@@ -69,7 +69,7 @@ void *__kmap_atomic(struct page *page)
 	 * With debugging enabled, kunmap_atomic forces that entry to 0.
 	 * Make sure it was indeed properly unmapped.
 	 */
-	BUG_ON(!pte_none(*(TOP_PTE(vaddr))));
+	BUG_ON(!pte_none(get_top_pte(vaddr)));
 #endif
 	/*
 	 * When debugging is off, kunmap_atomic leaves the previous mapping
@@ -119,7 +119,7 @@ void *kmap_atomic_pfn(unsigned long pfn)
 	idx = type + KM_TYPE_NR * smp_processor_id();
 	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
 #ifdef CONFIG_DEBUG_HIGHMEM
-	BUG_ON(!pte_none(*(TOP_PTE(vaddr))));
+	BUG_ON(!pte_none(get_top_pte(vaddr)));
 #endif
 	set_top_pte(vaddr, pfn_pte(pfn, kmap_prot));
 
@@ -129,11 +129,9 @@ void *kmap_atomic_pfn(unsigned long pfn)
 struct page *kmap_atomic_to_page(const void *ptr)
 {
 	unsigned long vaddr = (unsigned long)ptr;
-	pte_t *pte;
 
 	if (vaddr < FIXADDR_START)
 		return virt_to_page(ptr);
 
-	pte = TOP_PTE(vaddr);
-	return pte_page(*pte);
+	return pte_page(get_top_pte(vaddr));
 }