le_audio: Add double CIS source ASE only scenario

Patch extends possibility to set up double microphone on different CISes
scenario.

Test: atest bluetooth_le_audio_client_test
Sponsor: @jpawlowski
Bug: 229802353
Change-Id: I574790c7d85b102844aa57b6039a2f9ff73187f9
(cherry picked from commit 407570eb902865582d5b2af09417fb2b83726512)