LoongArch: Replace kmap_atomic() with kmap_local_page() in copy_user_highpage()

Replace kmap_atomic()/kunmap_atomic() calls with kmap_local_page()/
kunmap_local() in copy_user_highpage() which can be invoked from both
preemptible and atomic context [1].

[1] https://lore.kernel.org/all/20201029222652.302358281@linutronix.de/Suggested-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/mm/init.c

@@ -43,11 +43,11 @@ void copy_user_highpage(struct page *to, struct page *from,
 {
 	void *vfrom, *vto;
 
-	vto = kmap_atomic(to);
-	vfrom = kmap_atomic(from);
+	vfrom = kmap_local_page(from);
+	vto = kmap_local_page(to);
 	copy_page(vto, vfrom);
-	kunmap_atomic(vfrom);
-	kunmap_atomic(vto);
+	kunmap_local(vfrom);
+	kunmap_local(vto);
 	/* Make sure this page is cleared on other CPU's too before using it */
 	smp_wmb();
 }