tests: bluetooth: tester: add nrf54l15 configs

Added:
nrf545pdk_nrf5415_cpuapp.overlay: Choose uart20 hwfc 115200
nrf54l15pdk_nrf54l15_cpuapp.conf

Signed-off-by: Aytürk Düzen <ayturk.duzen@nordicsemi.no>
2 files changed