mtd: nand: mxc: Fix failed/corrected values for v1 controllers

The v1 controller code has several flaws:
- We do not forward the number of corrected bitflips to the upper layers
- For 2k page NAND chips only the status results from the fourth subpage
  read are evaluated, so ECC failures in the other subpages remain
  uncovered
- When there are uncorrectable errors we have to increase the statistics
  counter, but still have to return successfully. Currently we return
  an error

This patch fixes this by introducing a v1 specific read_page function.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>