dt-bindings: serial: allow naming of Bluetooth with GPS children

Some devices attached over UART combine Bluetooth and GNSS/GPS receiver,
so allow "bluetooth-gnss" naming of children nodes.

Link: https://lore.kernel.org/all/20231004070309.2408745-1-andreas@kemnade.info/
Suggested-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20231005093247.128166-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>