use case for register_pstore_blk?

[Christoph Hellwig]

Hi WeiXiong, hi Kees,

what is the use case for the code added in commit 17639f67c1d6 
("pstore/blk: Introduce backend for block devices").

This still doesn't have a user, and the API looks really odd to me.
By our normal kernel rules we should not add new exports without
users and this should probably be reverted for the 5.9 release.