mtd: spi-nor: Bring flash params init together

Bring all flash parameters default initialization in
spi_nor_legacy_params_init().

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>