mtd: rawnand: Drop OOB_FIRST placement scheme

This scheme has been introduced for the Davinci controller and means
that the OOB area must be read *before* the rest of the data. This has
nothing to do with the ECC in OOB placement as it could be understood
and most importantly, there is no point in having this function out of
the Davinci NAND controller driver. A DT property for this scheme has
been added but never used, even by the Davinci driver which only uses
this scheme to change the default nand_read_page().

Move the main read_page() helper into the Davinci driver and remove
the remaining boilerplate.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200526195633.11543-4-miquel.raynal@bootlin.com