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: Xishi 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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;