mtd: mtdpart: implement proper partition handling

Instead of collecting partitions in a flat list, create a hierarchy
within the mtd_info structure: use a partitions list to keep track of
the partitions of an MTD device (which might be itself a partition of
another MTD device), a pointer to the parent device (NULL when the MTD
device is the root one, not a partition).

By also saving directly in mtd_info the offset of the partition, we
can get rid of the mtd_part structure.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index fb1d68d..fb6c779 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -426,6 +426,8 @@
 	mtd->index = i;
 	mtd->usecount = 0;
 
+	INIT_LIST_HEAD(&mtd->partitions);
+
 	/* default value if not set by driver */
 	if (mtd->bitflip_threshold == 0)
 		mtd->bitflip_threshold = mtd->ecc_strength;