tests: drivers: dma: support ztest for DMA driver on RA boards

Add .overlay and .conf files for Renesas RA boards to enable
ztest for the DMA driver in:
- tests/drivers/dma/chan_blen_transfer
- tests/drivers/dma/loop_transfer

Signed-off-by: Khanh Nguyen <khanh.nguyen.wz@bp.renesas.com>