mtd: nand: drop unnecessary partition parser data

All of these drivers set up a parser data struct just to communicate DT
partition data. This field has been deprecated and is instead supported
by telling nand_scan_ident() about the 'flash_node'.

This patch:
 * sets chip->flash_node for those drivers that didn't already (but used
   OF partitioning)
 * drops the parser data
 * switches to the simpler mtd_device_register() where possible, now
   that we've eliminated one of the auxiliary parameters

Now that we've assigned chip->flash_node for these drivers, we can
probably rely on nand_dt_init() to do more of the DT parsing for us, but
for now, I don't want to fiddle with each of these drivers. The parsing
is done in duplicate for now on some drivers. I don't think this should
break things. (Famous last words.)

(Rolled in some changes by Boris Brezillon)

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>