mtd: rawnand: marvell: Fix and update kerneldoc

Fix kerneldoc comments and add missing documentation for members to fix
W=1 compile warnings like:

  drivers/mtd/nand/raw/marvell_nand.c:251: warning:
    cannot understand function prototype: 'struct marvell_hw_ecc_layout '

  drivers/mtd/nand/raw/marvell_nand.c:342: warning:
    Function parameter or member 'layout' not described in 'marvell_nand_chip'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200901142535.12819-5-krzk@kernel.org