dmaengine: fsl-edma: extract common fsl-edma code (no changes in behavior intended)

This patch adds a new fsl-edma-common module to allow new
mcf-edma module code to use most of the fsl-edma code.

Signed-off-by: Angelo Dureghello <angelo@sysam.it>
Tested-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>