mtd: rawnand: Create a legacy struct and move ->IO_ADDR_{R, W} there

We regularly have new NAND controller drivers that are making use of
fields/hooks that we want to get rid of but can't because of all the
legacy drivers that we might break if we do.

So, instead of removing those fields/hooks, let's move them to a
sub-struct which is clearly documented as deprecated.

We start with the ->IO_ADDR_{R,W] fields.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

arch/arm/mach-pxa/em-x270.c

@@ -288,7 +288,7 @@ static void nand_cs_off(void)
 static void em_x270_nand_cmd_ctl(struct nand_chip *this, int dat,
 				 unsigned int ctrl)
 {
-	unsigned long nandaddr = (unsigned long)this->IO_ADDR_W;
+	unsigned long nandaddr = (unsigned long)this->legacy.IO_ADDR_W;
 
 	dsb();
 
@@ -308,9 +308,9 @@ static void em_x270_nand_cmd_ctl(struct nand_chip *this, int dat,
 	}
 
 	dsb();
-	this->IO_ADDR_W = (void __iomem *)nandaddr;
+	this->legacy.IO_ADDR_W = (void __iomem *)nandaddr;
 	if (dat != NAND_CMD_NONE)
-		writel(dat, this->IO_ADDR_W);
+		writel(dat, this->legacy.IO_ADDR_W);
 
 	dsb();
 }