NAND: Scan bad blocks lazily.

Rather than scanning on boot, scan upon the first attempt to check the
badness of a block.  This speeds up boot when not using NAND, and reduces
the likelihood of needing to reflash via JTAG if NAND becomes
nonfunctional.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>

include/linux/mtd/nand.h

@@ -204,6 +204,8 @@ typedef enum {
    (e.g. because it needs them DMA-coherent */
 #define NAND_OWN_BUFFERS	0x00040000
 /* Options set by nand scan */
+/* bbt has already been read */
+#define NAND_BBT_SCANNED	0x40000000
 /* Nand scan has allocated controller struct */
 #define NAND_CONTROLLER_ALLOC	0x80000000