selftests/bpf: add test_spec_readahead_xfs_file to support specail async readahead

hulk inclusion
category: feature
bugzilla: 173267
CVE: NA
---------------------------

For hibench applications, likely kmeans, wordcount, terasort,
we can try to use this bpf tool to improve io performance.

Usage:
	make -C bpf
	./test_xfs_file spec_readahead

Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>