Use helper function free_highmem_page() to free highmem pages into
the buddy system.

Also fix a bug that totalhigh_pages should be increased when freeing
a highmem page into the buddy system.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>