LU-11698 libcfs: Add checksum speed under /sys/fs

LU-11698 libcfs: Add checksum speed under /sys/fs

This patch adds total of registered checksum and all
registered checksum names along with their speed under
/sys/kernel/debug/lustre/checksum_speed

TestCase sanity/77m added.

Sample output:
$ lctl get_param checksum_speed
checksum_speed=adler32: 1955
crc32: 2423
crc32c: 14035

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: If125032e35bfd9221eb66e6f77bf7e3753ffcc0f
Reviewed-on: https://review.whamcloud.com/43943
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>