scsi: ufs: sysfs: flags

This patch introduces a sysfs group entry for the UFS flags. The group adds
"flags" folder under the UFS driver sysfs entry
(/sys/bus/platform/drivers/ufshcd/*). The flags are shown as boolean value
("true" or "false"). The full information about the UFS flags 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>