tests: drivers: dma: Enable for board sgrm

This allows to run the test 'chan_blen_transfer' and 'loop_transfer' on
the sgrm board.

The functionality tested in `chan_link_transfer` and `scatter_gather` is
not (yet) supported by the Si32 DMA driver, and those tests therefore
not enabled.

Signed-off-by: Reto Schneider <reto.schneider@husqvarnagroup.com>