dmaengine: edma: add protection for variables to avoid corruption

Changes include support for

i) Add protection for variables being used across functions to avoid
corruption.

ii) Updation of CB flag
EDMA hardware will start processing descriptors based on CB flag. During
high throughput conditions there can be a chance that CB flags get
updated even before memcpy of descriptor data element. Hence make sure
to set the CB flag post memcpy.

iii) Add support for dumping EDMA registers.

Change-Id: I97bba62b71536014ef8b3ceef2862654e98dc821
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>