mm/compaction: merge end_pfn boundary check in isolate_freepages_range

Merge the end_pfn boundary check for single page block forward and
multiple page blocks forward to avoid do twice boundary check for multiple
page blocks forward.

Link: https://lkml.kernel.org/r/20230803094901.2915942-3-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>