mtd: rawnand: mxc: separate page read from ecc calc

Our read_page hook currently reads out a page and also counts and
returns the number of bitflips. In upcoming exec_op conversion we'll
need to read the page data in exec_op, but the bitflip information
will be needed in mxc_nand_read_page(). To ease exec_op conversion
separate the page read out from the bitflip evaluation.

For the v2/v3 controllers we can leave the bitflip information in the
status register for later evaluation. For the v1 controller this is
not possible, because the status register is overwritten with each
subpage read. We therefore store the bitflip information in the private
data.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240522-mtd-nand-mxc-nand-exec-op-v4-1-75b611e0ac44@pengutronix.de