mtd: rawnand: atmel: Add message on DMA usage

Like for other atmel drivers (serial, crypto, mmc, …), too.

Signed-off-by: Alexander Dahl <ada@thorsis.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240828063707.73869-1-ada@thorsis.com