DMAENGINE: ste_dma40: code clean-up

This patch includes non functional code clean up changes,
file header updates and a few magic numbers got defined.

Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>