arm64: dts: freescale: Add support for Variscite DART-MX91

arm64: dts: freescale: Add support for Variscite DART-MX91

Add device tree support for the Variscite DART-MX91 system on module.
This SOM is designed to be used with various carrier boards.

The module includes:
- NXP i.MX91 MPU processor
- Up to 2GB of LPDDR4 memory
- Up to 128GB of eMMC storage memory
- Integrated 10/100/1000 Mbps Ethernet Transceiver
- Codec audio WM8904
- WIFI6 dual-band 802.11ax/ac/a/b/g/n with optional 802.15.4 and Bluetooth

Only SOM-specific peripherals are enabled by default. Carrier board
specific interfaces are left disabled to be enabled in the respective
carrier board device trees.

Link: https://variscite.com/system-on-module-som/i-mx-9/i-mx-91/dart-mx91/
Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>