fsldma: remove unused structure members

Remove some unused members from the fsldma data structures. A few trivial
uses of struct resource were converted to use the stack rather than keeping
the memory allocated for the lifetime of the driver.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>