dt-bindings: gnss: add u-blox binding

Add binding for u-blox GNSS receivers.

Note that the u-blox product names encodes form factor (e.g. "neo"),
chipset (e.g. "8") and variant (e.g. "q"), but that only formfactor and
chipset is used for the compatible strings (for now).

Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>