dmaengine: gpi: optimize completion event processing

To increase gpi performance, optimize event processing
path. First optimization is to disable verbose logging
on production settings, second optimization is to send
completion callback from same processing context instead
of going thru dma-engine vc framework to eliminate
additional scheduling delays.

CRs-Fixed: 2165975
Change-Id: I1baaae16a0dc4b57651483050a567000c35ba5e2
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>