[SCSI] qla2xxx: Extend the 'fw_dump' SYSFS node the ability to initiate a firmware dump.

The user-initiated dump can be a useful tool in triaging complex
ISP and FC issues.

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