avr32: at32ap700x: don't rely on default DMA masters

In future we are going to remove the defaults of AHB masters from dw_dmac
driver. It means each user have to supply proper source and destination masters
by itself explicitly.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>