[SCSI] qla2xxx: Add NVRAM 'Disable Serdes' bit support.

The host section of ISP24xx NVRAMs contain a new bit which
allows a user to selectively disable ports of an HBA.  These
ports (hosts) will not be presented to the midlayer.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>