LU-16231 misc: rename lprocfs_stats functions

LU-16231 misc: rename lprocfs_stats functions

Rename lprocfs_{alloc,register,clear,free}_stats() to be
lprocfs_stats_*() so these functions can be found more easily
in relation to struct lprocfs_stats.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I671284a86ee2a1fd3c58da75923f9467e72540e5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48847
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ellis Wilson <elliswilson@microsoft.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>