scsi: qla2xxx: Further limit FLASH region write access from SysFS

Recent ISPs have larger and more complex flash-write semantics
(secure-access and signing). The BSG interfaces support these semantics for
all ISPs and is exclusively used by QLogic user-space tools. Limit
flash-write operations to ISPs <= 25xx.

Signed-off-by: Andrew Vasquez <andrewv@marvell.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>