scsi: lpfc: Add 64G link speed support

The G7 adapter supports 64G link speeds. Add support to the driver.

In addition, a small cleanup to replace the odd bitmap logic with
a switch case.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>