Add module parameters to allow load time configuration of DMA channels.

Depending on application, performance of DMA data transfers can benefit
from adjusted sizes of buffer descriptor ring and/or transaction
requests queue.

Having HW DMA channel selector mask allows to define which channels
(from seven available) are controlled by the mport device driver and
reserve some of them for direct use by other drivers.

Link: http://lkml.kernel.org/r/1469125134-16523-5-git-send-email-alexandre.bounine@idt.comSigned-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Tested-by: Barry Wood <barry.wood@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
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>