dma: dw: Add a debug utility function

Add a helper function to dump the GPDMA SHIM and channel registers for
debug along with a config option to enable it.

Co-developed-by: Tom Burdick <thomas.burdick@intel.com>
Singed-off-by: Tom Burdick <thomas.burdick@intel.com>
Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>