scsi: qla2xxx: Add Device ID for ISP28XX

This patch adds PCI device ID ISP28XX for Gen7 support.  Also signature
determination for primary/secondary flash image for ISP27XX/28XX is aded as
part of Gen7 support.

Signed-off-by: Joe Carnuccio <joe.carnuccio@cavium.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>