mtd: spi-nor: Drop quad_enable() from 'struct spi-nor'

All flash parameters and settings should reside inside
'struct spi_nor_flash_parameter'. Drop the local copy of
quad_enable() and use the one from 'struct spi_nor_flash_parameter'.

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