mtd: nand: move NAND_CREATE_EMPTY_BBT flag

The NAND_CREATE_EMPTY_BBT flag was added by commit:
  453281a9
  mtd: nand: introduce NAND_CREATE_EMPTY_BBT
This flag is not used within the kernel and not explained well, so I
took the liberty to edit its comments.

Also, this is a BBT-related flag (and closely tied with NAND_BBT_CREATE)
so I'm moving it to bbm.h next to NAND_BBT_CREATE, thus requiring that
we use the flag in nand_chip.bbt_options, *not* in nand_chip.options.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/nand/nand_bbt.c

@@ -970,7 +970,7 @@ static int check_create(struct mtd_info *mtd, uint8_t *buf, struct nand_bbt_desc
 			continue;
 
 		/* Create the table in memory by scanning the chip(s) */
-		if (!(this->options & NAND_CREATE_EMPTY_BBT))
+		if (!(this->bbt_options & NAND_CREATE_EMPTY_BBT))
 			create_bbt(mtd, buf, bd, chipsel);
 
 		td->version[i] = 1;

include/linux/mtd/bbm.h

@@ -86,6 +86,13 @@ struct nand_bbt_descr {
 #define NAND_BBT_VERSION	0x00000100
 /* Create a bbt if none exists */
 #define NAND_BBT_CREATE		0x00000200
+/*
+ * Create an empty BBT with no vendor information. Vendor's information may be
+ * unavailable, for example, if the NAND controller has a different data and OOB
+ * layout or if this information is already purged. Must be used in conjunction
+ * with NAND_BBT_CREATE.
+ */
+#define NAND_CREATE_EMPTY_BBT	0x01000000
 /* Search good / bad pattern through all pages of a block */
 #define NAND_BBT_SCANALLPAGES	0x00000400
 /* Scan block empty during good / bad block scan */

include/linux/mtd/nand.h

@@ -228,8 +228,6 @@ typedef enum {
 #define NAND_OWN_BUFFERS	0x00040000
 /* Chip may not exist, so silence any errors in scan */
 #define NAND_SCAN_SILENT_NODEV	0x00080000
-/* Create an empty BBT with no vendor information if the BBT is available */
-#define NAND_CREATE_EMPTY_BBT		0x01000000
 
 /* Options set by nand scan */
 /* Nand scan has allocated controller struct */