Bluetooth: Host: CMake dependency for Mesh Bsim

Links host to mbedTLS library if Bluetooth Mesh is enabled, and
CONFIG_BT_TESTING=y.

Bluetooth Mesh has test dependencies in the host.
In order to compile Bsim tests with these test features
and PSA enabled, the libraries must be linked.

Signed-off-by: Anders Storrø <anders.storro@nordicsemi.no>