scsi: ufs: sysfs: unit descriptor

This patch introduces a sysfs group entry for the UFS unit descriptor
parameters. The group adds "unit_descriptor" folder under the corresponding
SCSI device sysfs entry (/sys/class/scsi_device/*/device/). The parameters
are shown as hexadecimal numbers. The full information about the parameters
could be found at UFS specifications 2.1.

Signed-off-by: Stanislav Nijnikov <stanislav.nijnikov@wdc.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>