Bluetooth: Controller: Default stream count based upon app configs

When building ISO applications on a device that has the host
and controller on the same core, the application developer
shouldn't have to set controller specific configurations.

Without this change the samples iso_receive and iso_broadcast
will fail to run on NRF52 series devices as the samples
try to set up two streams but the controller is configured
to support only one.

Controller unit tests that were previously only enabling the
controller specific ISO configurations now also enable the
top-level ISO configurations to ensure that the default
stream count is properly configured.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>