mtd: rawnand: brcmnand: Don't default to edu transfer

When flash-dma is absent do not default to using flash-edu.
Make sure flash-edu is enabled before setting EDU transfer
function.

Fixes: a5d53ad2 ("mtd: rawnand: brcmnand: Add support for flash-edu for dma transfers")
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/20200612212902.21347-2-kdasu.kdev@gmail.com