scsi: fc: Update documentation of sysfs nodes for FPIN stats

Update documentation for sysfs nodes within:

/sys/class/fc_host
/sys/class/fc_remote_ports

Link: https://lore.kernel.org/r/20201021092715.22669-6-njavali@marvell.com
Reviewed-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Shyam Sundar <ssundar@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>