arm64: dts: imx8mm-beacon: Resync imx8mm-beacon-som with 5.11-rc4

In order to support the QSPI chip on the SOM, the Flexspi bus
needs to be configured to talk with the SPI chip.
Resync the som device tree with 5.11-rc4

Signed-off-by: Adam Ford <aford173@gmail.com>
Acked-by: Peng Fan <peng.fan@nxp.com>