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.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>