mtd: fsl-quadspi: use automatic spi-nor detection

We don't really need the flash information from the device tree here.
Let's stick with autodetection here instead.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Han Xu <han.xu@freescale.com>
Tested-by: Han Xu <han.xu@freescale.com>