scsi: fc: Add FPIN statistics to fc_host and fc_rport objects

Add a structure for holding FPIN statistics, for host & rport respectively,
and add associated sysfs nodes:

        /sys/class/fc_host/hostXX/statistics/
        /sys/class/fc_remote_ports/rport-XX\:Y-Z/statistics/

Link: https://lore.kernel.org/r/20201021092715.22669-3-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>