mtd: nand: sharpsl: Add partition parsers platform data

With the introduction of sharpslpart partition parser we can now read the
offsets from NAND: we specify the list of the parsers as platform data, with
cmdlinepart and ofpart parsers first allowing to override the part. table
written in NAND. This is done in the board files using this driver.

Thus, we need to extend sharpsl_nand_platform_data to consider the partition
parsers.

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>