mm/arch: use __free_reserved_page() to simplify the code

Use __free_reserved_page() to simplify the code in arch.

It used split_page() in consistent_alloc()/__dma_alloc_coherent()/dma_alloc_coherent(),
so page->_count == 1, and we can free it safely.

__free_reserved_page()
	ClearPageReserved()
	init_page_count()  // it won't change the value
	__free_page()
Signed-off-by: NXishi Qiu <qiuxishi@huawei.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/metag/kernel/dma.c

@@ -305,9 +305,7 @@ void dma_free_coherent(struct device *dev, size_t size,
 
 			if (pfn_valid(pfn)) {
 				struct page *page = pfn_to_page(pfn);
-				ClearPageReserved(page);
-
-				__free_page(page);
+				__free_reserved_page(page);
 				continue;
 			}
 		}

arch/microblaze/mm/consistent.c

@@ -176,8 +176,7 @@ void consistent_free(size_t size, void *vaddr)
 	page = virt_to_page(vaddr);
 
 	do {
-		ClearPageReserved(page);
-		__free_page(page);
+		__free_reserved_page(page);
 		page++;
 	} while (size -= PAGE_SIZE);
 #else
@@ -194,9 +193,7 @@ void consistent_free(size_t size, void *vaddr)
 			pte_clear(&init_mm, (unsigned int)vaddr, ptep);
 			if (pfn_valid(pfn)) {
 				page = pfn_to_page(pfn);
-
-				ClearPageReserved(page);
-				__free_page(page);
+				__free_reserved_page(page);
 			}
 		}
 		vaddr += PAGE_SIZE;

arch/powerpc/mm/dma-noncoherent.c

@@ -287,9 +287,7 @@ void __dma_free_coherent(size_t size, void *vaddr)
 			pte_clear(&init_mm, addr, ptep);
 			if (pfn_valid(pfn)) {
 				struct page *page = pfn_to_page(pfn);
-
-				ClearPageReserved(page);
-				__free_page(page);
+				__free_reserved_page(page);
 			}
 		}
 		addr += PAGE_SIZE;