nand: Move the sub-page read support enable to a flag

Use a flag instead of a hard-coded macro so that sub-page reads can be
enabled in other cases (such as on-die ecc).

This is the same as a5ff4f102937a3492bca4a9ff0c341d78813414c in Linux

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index d3b71a5..a2d06be 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1245,7 +1245,8 @@
 			if (unlikely(ops->mode == MTD_OOB_RAW))
 				ret = chip->ecc.read_page_raw(mtd, chip,
 							      bufpoi, page);
-			else if (!aligned && NAND_SUBPAGE_READ(chip) && !oob)
+			else if (!aligned && NAND_HAS_SUBPAGE_READ(chip) &&
+			    !oob)
 				ret = chip->ecc.read_subpage(mtd, chip,
 							col, bytes, bufpoi);
 			else
@@ -1256,7 +1257,7 @@
 
 			/* Transfer not aligned data */
 			if (!aligned) {
-				if (!NAND_SUBPAGE_READ(chip) && !oob &&
+				if (!NAND_HAS_SUBPAGE_READ(chip) && !oob &&
 				    !(mtd->ecc_stats.failed - stats.failed))
 					chip->pagebuf = realpage;
 				memcpy(buf, chip->buffers->databuf + col, bytes);
@@ -3150,6 +3151,10 @@
 	/* Invalidate the pagebuffer reference */
 	chip->pagebuf = -1;
 
+	/* Large page NAND with SOFT_ECC should support subpage reads */
+	if ((chip->ecc.mode == NAND_ECC_SOFT) && (chip->page_shift > 9))
+		chip->options |= NAND_SUBPAGE_READ;
+
 	/* Fill in remaining MTD driver data */
 	mtd->type = MTD_NANDFLASH;
 	mtd->flags = (chip->options & NAND_ROM) ? MTD_CAP_ROM :