arm64: Defer dcache flush in __cpu_copy_user_page

Defer dcache flushing to __sync_icache_dcache by calling
flush_dcache_page which clears PG_dcache_clean flag.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ashok Kumar <ashoks@broadcom.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/mm/copypage.c

@@ -24,8 +24,9 @@
 
 void __cpu_copy_user_page(void *kto, const void *kfrom, unsigned long vaddr)
 {
+	struct page *page = virt_to_page(kto);
 	copy_page(kto, kfrom);
-	__flush_dcache_area(kto, PAGE_SIZE);
+	flush_dcache_page(page);
 }
 EXPORT_SYMBOL_GPL(__cpu_copy_user_page);