DMAENGINE: ste_dma40: no disabled phy channels on ux500

Make sure we have no disabled physical channels when we start on
the ux500 machines.

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>