mtd: rawnand: brcmnand: rename v4 registers

These registers are also used on v3.3.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200522121524.4161539-2-noltari@gmail.com