rapidio/tsi721_dma: fix synchronization issues

Fix synchronization issues found during testing using multiple DMA
transfer requests to the same channel:

 - lost MSI-X interrupt notifications
 - non-synchronized attempts to start DMA channel HW resulting in error
   message from the driver
 - cookie tracking/update race conditions resulting in incorrect DMA
   transfer status report

Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Reported-by: Barry Wood <barry.wood@idt.com>
Tested-by: Barry Wood <barry.wood@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Andre van Herk <andre.van.herk@prodrive-technologies.com>
Cc: Barry Wood <barry.wood@idt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>