mtd: spi-nor: store .n_banks in struct spi_nor_flash_parameter

mtd: spi-nor: store .n_banks in struct spi_nor_flash_parameter

First, fixups might want to replace the n_banks parameter, thus we need
it in the (writable) parameter struct. Secondly, this way we can have a
default in the core and just skip setting the n_banks in the flash_info
database. Most of the flashes doesn't have more than one bank.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20230807-mtd-flash-info-db-rework-v3-7-e60548861b10@kernel.org
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>