LU-13729 osd-ldiskfs: race access to iam_formats during setup

LU-13729 osd-ldiskfs: race access to iam_formats during setup

It might be possible during OST mounting, two targets reach
iam_format_guess() at the same time, if @initialized is 0,
they both access iam_lxx_format_init(), however list operation
inside is not protected by any locking which cause list corruptions
finally.

We could fix this by doing formats registration in module init,
since there are only two formats, just remove pointless list.

Lustre-change: https://review.whamcloud.com/39213
Lustre-commit: 54d0f5de911af52e7f2a978c4b6cd158fed87dc5

Signed-off-by: Wang Shilong <wshilong@ddn.com>
Change-Id: I6dd5a4d1297792b47fb4b94052465a7e0f9123aa
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-on: https://review.whamcloud.com/44356
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Wang Shilong <wangshilong1991@gmail.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>