arm64: tegra: Drop serial clock-names and reset-names

The serial node does not use clock-names and reset-names:

  tegra234-sim-vdk.dtb: serial@3100000: Unevaluated properties are not allowed ('clock-names', 'reset-names' were unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>