Add rules for building src/tls/libtls.a and use it with eap_example

Add rules for building src/tls/libtls.a and use it with eap_example

eap_example is now using src/crypto/libcrypto.a and src/tls/libtls.a
instead of providing own rules for building the files for these
components. TLS library selection is temporarily disabled for
eap_example (it will be built using internal crypto/TLS), but the
configuration option for this will eventually be restored with a new
libcrypto.a configuration option.