mtd: rawnand: brcmnand: Add platform data structure for BCMA

Update the BCMA's chipcommon nand flash driver to detect which
chip-select is used and pass that information via platform data to the
brcmnand driver. Make sure that the brcmnand platform data structure is
always at the beginning of the platform data of the "nflash" device
created by BCMA to allow brcmnand to safely de-reference it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220107184614.2670254-7-f.fainelli@gmail.com