samples: Bluetooth: hci_uart/hci_ipc: CI coverage for nRF53+nRF21 FEM

Add CI coverage for nRF5340 plus nRF21540 FEM usage in
hci_uart plus hci_ipc samples.

The overlay values are inspired from:
https://github.com/nrfconnect/sdk-nrf/tree/


85307a9ca0fb6ba8c61f4bd05b7f866cde42612f/boards/shields/nrf21540ek

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>