DMAENGINE: ste_dma40: added support for link jobs in hw

If a new job is added on a physical channel that already has
a job, the new job is linked in hw to the old job instead of
queueing up the jobs.

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>