arm64: dts: Add spi-[tx/rx]-bus-width for the FSL QSPI controller

We will move the FSL QSPI driver to the SPI framework soon. To
prepare and to make sure the full buswidth is used (as it is with
the current driver), let's add the right properties.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>