Revert "Revert "ext4: Allow parallel DIO reads""

hulk inclusion
category: feature
bugzilla: 185871, https://gitee.com/openeuler/kernel/issues/I4MIQ0


CVE: NA

---------------------------

This reverts commit bb24e7e6.

In order to improve the dio reads performance, we enable the
parallel dio reads.

And make it configuratable

Conflict:
	fs/ext4/Kconfig
	fs/ext4/inode.c

Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>