Firmware update fails with: status x17 add_status x56 on the final write

If multiple DMA buffers are used for the download, some firmware revs
have difficulty with signatures and crcs split across the dma buffer
boundaries.  Resolve by making all writes be a single 4k page in length.
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>