nrf: clock control: nrf5340: using CLOCK_CONTROL_NRF_K32SRC_RC results in build failure

[ioannisg]

Describe the bug
It appears to me that setting CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y in nRF5340 builds for Application MCU results in build failure.

To Reproduce
Steps to reproduce the behavior:

Try hello_world sample with CLOCK_CONTROL_NRF_K32SRC_RC=y

Build for nRF5340 CPUAPP

1. mkdir build; cd build
2. cmake -DBOARD=board\nrf5340pdk_nrf5340_cpuapp
3. make
4. See error

Expected behavior
Shall be able to build.

Impact
Cannot use RC oscillator on nRF5340

If this configuration is not supposed to be a valid one, i believe it should be blocked in Kconfig level.