arm64: dts: mediatek: split off navi from rauru

If only one FDT is contained in a FIT image, the Chromebook bootloader will simply pick that FDT. However, if multiple are included, the bootloader picks a device tree blob from the supplied signed FIT image based on matching compatibles, meaning that if a device's compatible doesn't have any matches with the bootloader's compatibles, it seemingly either doesn't pick it or will pick the first one which may be wrong.

Long story short, since the Google Navi production hardware doesn't have "google,rauru" in its list of compatibles in the firmware, despite this quite literally being the very case where one would want to use compatibles as a list with fallbacks, we need a separate device tree for it. This is fine, as we're going to require a separate DT anyway, since the navi units have some differences from the rauru units, and each navi SKU then again has some variations from the base navi tree.

Reorganise the rauru.dtsi and rauru-rev0.dts trees a little to make sure all rauru-rev0 specific nodes really are in rev0. Then, add a navi .dtsi, and a dts file for navi SKU2. Other navi SKUs may lack the fingerprint reader or include a touchscreen or do both.

For upstream, we may want to have "model" set to the brand name the device is sold under if it ends up being just one brand device per SKU. Letting the dust settle before doing that may be a better idea however.

Technically, "model" could be a string list as per the DT schema, but robher cautioned me that it's somewhat ill-defined what that would mean, and dtc raises a warning about it as well.

Note: new dtb also needs to be included in the mkimage command in our chromebook image pipeline after this is merged for the images to actually boot on the Lenovo Chromebook Plus (14", Gen 10)