[nrf noup]: fix mbedtls_psa_crypto_configure_entropy_sources symbol

-This is a [nrf noup] as we are using MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG
 more actively then Oberon PSA core. This commit ensures we are only
 enabling mbedtls_psa_crypto_configure_entropy_sources when
 entropy/rng is not enabled by external sources

Signed-off-by: Frank Audun Kvamtrø <frank.kvamtro@nordicsemi.no>

library/psa_crypto.c

@@ -5363,6 +5363,7 @@ psa_status_t psa_generate_key(const psa_key_attributes_t *attributes,
 /* Module setup */
 /****************************************************************/
 
+#if !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
 psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
     void (* entropy_init)(mbedtls_entropy_context *ctx),
     void (* entropy_free)(mbedtls_entropy_context *ctx))
@@ -5371,6 +5372,7 @@ psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
     (void)entropy_free;
     return PSA_SUCCESS;
 }
+#endif
 
 void mbedtls_psa_crypto_free(void)
 {