Add missing pull-up for RX pin in nrf54h20dk dual uart configuration.
Lack of pull-up was causing test failures.
Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>
Adding a separate overlay for nrf54l15 flpr is required because
running tests on console uart fails.
Signed-off-by: Jakub Zymelka <jakub.zymelka@nordicsemi.no>