mtd: rawnand: brcmnand: Add support for flash-edu for dma transfers

Legacy mips soc platforms that have controller v5.0 and 6.0 use
flash-edu block for dma transfers. This change adds support for
nand dma transfers using the EDU block.
Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200122213313.35820-4-kdasu.kdev@gmail.com