LeAudio: Encapsulate CIS counting strategy

This change moves the CIS counting logic to a more appropriate place.
le_audio_types.h/cc is for more generic data structures and not for a
CIS selection logic based on the group topology. This fits naturally
into the CigConfiguration inside the LeAudioDeviceGroup instance.

Bug: 388499616
Test: atest bluetooth_le_audio_test
Flag: Exempt; No logical changes - functionality moved
Change-Id: I82108061909ce02143c39c27fd224c4c9b7b4d5d