DMAENGINE: move COH901318 to arch_initcall

After moving the PL022 driver to subsys_initcall() due to the need
of having stuff like regulators on the other end of the SPI link,
I noticed that the COH901318 DMA engine will get probed before
the DMA engine, so move it to an arch_initcall().

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