fsldma: use PCI Read Multiple command

By default, the Freescale 83xx DMA controller uses the PCI Read Line
command when reading data over the PCI bus. Setting the controller to use
the PCI Read Multiple command instead allows the controller to read much
larger bursts of data, which provides a drastic speed increase.

The slowdown due to using PCI Read Line was only observed when a PCI-to-PCI
bridge was between the devices trying to communicate.

A simple test driver showed an increase from 4MB/sec to 116MB/sec when
performing DMA over the PCI bus. Using DMA to transfer between blocks of
local SDRAM showed no change in performance with this patch. The dmatest
driver was also used to verify the correctness of the transfers, and showed
no errors.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Acked-by: Timur Tabi <timur@freescale.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>