Bluetooth: Audio: Move some unicast shell commands to also support server

Some of the unicast audio shell commands were guarded by
CONFIG_BT_AUDIO_UNICAST_CLIENT and only usable by the client.

This moves some of the commands to a CONFIG_BT_AUDIO_UNICAST
guard instead, so that they are usable for builds with just
the server.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>