fsldma: rename fsl_chan to chan

The name fsl_chan seems too long, so it has been shortened to chan. There
are only a few places where the higher level "struct dma_chan *chan" name
conflicts. These have been changed to "struct dma_chan *dchan" instead.
Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>