adjust OSBA discrete-coding x-over BR[non BE][non-io]

• Related issues: #1072 (closed)
• Requested reviewers: @tyagiri

Reason why this change is needed

OSBA quality can be improved significantly when objects are coded discretely starting from lower bitrates

Description of the change

enable discrete coding from 96 kbps on for 1 object and from 128 kbps on for more objects

Affected operating points

OSBA 96 - 192 kbps