LU-13802 llite: add hybrid IO switch proc stats

LU-13802 llite: add hybrid IO switch proc stats

Hybrid IO switching proc stats are useful for telling us if
and why we switched to DIO.  They're also helpful for
writing tests.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <patrick.farrell@oracle.com>
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: I68649474cf11ffc445574fcca105a81fd6ecd458
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52596
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>