scsi: bnx2fc: Limit the IO size according to the FW capability

 - Reduce the sg_tablesize to 255.

 - Reduce the MAX BDs firmware can handle to 255.

 - Return IO to ML if BD goes more then 255 after split.

 - Correct the size of each BD split to 0xffff.

Signed-off-by: Saurav Kashyap <skashyap@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>