dmaengine: gpi: Add support to dump GPI registers by clients

This is to add gpi register dump support where clients can directly
call the API to dump GSI registers. This helps debug when GSI transfer
has any issue like timeout, no callback etc at the client driver and
want to dump register directly based on the need.

Change-Id: I1d9fadd51ccea166f2a486e84a8de47c134e435b
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>