scsi: qla1280: properly handle 64-bit DMA

CONFIG_HIGHMEM is not in fact an indicator for > 32-bit dma addressing
Given that the driver is a bit weird and wants a compile time selection
switch to checking CONFIG_ARCH_DMA_ADDR_T_64BIT instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>