mtd: edit comments on deprecation of ioctl ECCGETLAYOUT

There were some improvements and additions necessary in the
comments explaining of the expansion of nand_ecclayout, the
introduction of nand_ecclayout_user, and the deprecation of the
ioctl ECCGETLAYOUT.

Also, I found a better placement for the macro MTD_MAX_ECCPOS_ENTRIES;
next to the definition of MTD_MAX_OOBFREE_ENTRIES in mtd-abi.h. The macro
is really only important for the ioctl code (found in drivers/mtd/mtdchar.c)
but since there are small edits being made to the user-space header, I
figured this is a better location.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdchar.c

@@ -495,7 +495,7 @@ static int shrink_ecclayout(const struct nand_ecclayout *from,
 
 	memset(to, 0, sizeof(*to));
 
-	to->eccbytes = min((int)from->eccbytes, MTD_MAX_ECCPOS_ENTRIES_OLD);
+	to->eccbytes = min((int)from->eccbytes, MTD_MAX_ECCPOS_ENTRIES);
 	for (i = 0; i < to->eccbytes; i++)
 		to->eccpos[i] = from->eccpos[i];