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/board/socrates/nand.c b/board/socrates/nand.c
index 15e6ea6..a67d812 100644
--- a/board/socrates/nand.c
+++ b/board/socrates/nand.c
@@ -48,7 +48,7 @@
 static void sc_nand_write_buf(struct mtd_info *mtd, const u_char *buf, int len)
 {
 	int i;
-	struct nand_chip *this = mtd->priv;
+	struct nand_chip *this = mtd_to_nand(mtd);
 
 	for (i = 0; i < len; i++) {
 		out_be32(this->IO_ADDR_W,
@@ -88,7 +88,7 @@
 static void sc_nand_read_buf(struct mtd_info *mtd, u_char *buf, int len)
 {
 	int i;
-	struct nand_chip *this = mtd->priv;
+	struct nand_chip *this = mtd_to_nand(mtd);
 	int val;
 
 	val = (state & FPGA_NAND_ENABLE) | FPGA_NAND_CMD_READ;
@@ -105,7 +105,7 @@
  */
 static int sc_nand_device_ready(struct mtd_info *mtdinfo)
 {
-	struct nand_chip *this = mtdinfo->priv;
+	struct nand_chip *this = mtd_to_nand(mtdinfo);
 
 	if (in_be32(this->IO_ADDR_W) & FPGA_NAND_BUSY)
 		return 0; /* busy */