samples: Bluetooth: Audio sample board files cleanup

Clean up some of the board specific configuration files.
Removed all CONFIG_BT_CTLR* configs from the nRF5340
appcore conf files as that does not compile the controller.

Ensured that the ISO buffer in the controller for
nRF52840 can contain SDUs from all BAP LC3 minimum
requirements, as the controller does not yet
support segmentation of SDUs.

Also fixed a few bad configurations (broadcast sink not
enabling the sync support etc.).

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