mtd: nand: Add+use mtd_to/from_nand and nand_get/set_controller_data

These functions are part of the Linux 4.6 sync.  They are being added
before the main sync patch in order to make it easier to address the
issue across all NAND drivers (many/most of which do not closely track
their Linux counterparts) separately from other merge issues.

Signed-off-by: Scott Wood <oss@buserror.net>
diff --git a/drivers/mtd/nand/nand_util.c b/drivers/mtd/nand/nand_util.c
index 90bf798..9b61087 100644
--- a/drivers/mtd/nand/nand_util.c
+++ b/drivers/mtd/nand/nand_util.c
@@ -59,7 +59,7 @@
 	int percent_complete = -1;
 	const char *mtd_device = mtd->name;
 	struct mtd_oob_ops oob_opts;
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 
 	if ((opts->offset & (mtd->erasesize - 1)) != 0) {
 		printf("Attempt to erase non block-aligned data\n");
@@ -217,7 +217,7 @@
 {
 	int ret = 0;
 	int status;
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 
 	/* select the NAND device */
 	chip->select_chip(mtd, 0);
@@ -267,7 +267,7 @@
 	int ret = 0;
 	int chipnr;
 	int page;
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 
 	/* select the NAND device */
 	chipnr = (int)(offset >> chip->chip_shift);
@@ -314,7 +314,7 @@
 	int chipnr;
 	int status;
 	int page;
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 
 	debug("nand_unlock%s: start: %08llx, length: %zd!\n",
 		allexcept ? " (allexcept)" : "", start, length);