mtd: rawnand: vf610_nfc: make use of ->exec_op()

mtd: rawnand: vf610_nfc: make use of ->exec_op()

This reworks the driver to make use of ->exec_op() callback. The
command sequencer of the VF610 NFC aligns well with the new ops
interface.

The operations are translated to a NFC command code while filling
the necessary registers. Instead of using the special status and
read ID command codes (which require to read status/ID from
special registers instead of the regular data area) the driver
now now uses the main data buffer for all commands. This
simplifies the driver as no special casing is needed.

For control data (status byte, id bytes and parameter page) the
driver needs to reverse byte order for little endian CPUs since
the controller seems to store the bytes in big endian order in
the data buffer.

The current state seems to pass MTD tests on a Colibri VF61.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>