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>
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 03a1e95..fe8d77e 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -112,11 +112,11 @@
 
 #define MTD_MAX_OOBFREE_ENTRIES_LARGE	32
 #define MTD_MAX_ECCPOS_ENTRIES_LARGE	448
-#define MTD_MAX_ECCPOS_ENTRIES_OLD	64	/* Previous maximum */
 /*
- * Correct ECC layout control structure. This replaces old nand_ecclayout
- * (mtd-abi.h) that is exported via ECCGETLAYOUT ioctl. It should be expandable
- *  in the future simply by the above macros.
+ * Internal ECC layout control structure. For historical reasons, there is a
+ * similar, smaller struct nand_ecclayout_user (in mtd-abi.h) that is retained
+ * for export to user-space via the ECCGETLAYOUT ioctl.
+ * nand_ecclayout should be expandable in the future simply by the above macros.
  */
 struct nand_ecclayout {
 	__u32 eccbytes;