[SCSI] qla2xxx: Add Flash Descriptor Table layout support.

The Flash Descriptor Table (FDT) present on many recent HBAs
encodes flash accessing characteristics of the flash-part used on
the HBA.  Use this information during flash manipulation (writes)
rather than using specific hard-coded values based on queried
manufacturer and device IDs.

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