Resolve "Harmonize generate_comfort_noise_enc_*fx(), configureFdCngEnc_*fx()"

• Related issues: #2455 (closed)
• Requested reviewers:

Reason why this change is needed

Copy from the issue:

The function pairs

• configureFdCngEnc_fx() <-> configureFdCngEnc_ivas_fx()
• generate_comfort_noise_enc_fx() <-> generate_comfort_noise_enc_ivas_fx()

are almost identical. They could be harmonized with little effort.

Closes #2455 (closed)