dt-bindings: serial: restrict possible child node names

The re-usable serial.yaml schema matches every property with ".*"
pattern, thus any other schema referencing it will not report unknown
(unevaluated) properties. This hides several wrong properties. It is
a limitation of dtschema, thus provide a simple workaround: expect
children to be only of few names matching upstream usage (Bluetooth,
GNSS, GPS and MCU).

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230206092624.22922-4-krzysztof.kozlowski@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>