H6 has DMA controller which supports 16 channels.

Add a node for it.
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NClément Péron <peron.clem@gmail.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>