Introduce an array for debugfs attributes to make it easier to add new
debugfs attributes. Change the value of the inode.i_private pointer for
debugfs attributes from a pointer to the HBA data structure to a pointer to
the attribute description for the stats attribute. Store the HBA pointer in
the private data of the parent inode instead.

Link: https://lore.kernel.org/r/20211020214024.2007615-7-bvanassche@acm.orgAcked-by: Avri Altman <Avri.Altman@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>