Fixup: Don't reference legacy ECP curve identifier in config.h

TinyCrypt should be used as a replacement of legacy ECC. In particular,
there shouldn't be any use of identifiers from the legacy ECC module.

So far, there's the configuration option

  MBEDTLS_SSL_CONF_SINGLE_EC_GRP_ID

that's relevant if MBEDTLS_SSL_CONF_SINGLE_CURVE is set, and which in
this case must resolve to an identifier of type mbedtls_ecp_group_id
indicating which single curve to enable.

With the introduction of TinyCrypt, we must either change the type
of this option to mbedtls_uecc_group_id, or introduce a separate
compilation option.

In order to avoid type confusion, this commit follows tha latter
approach, introducing the configuration option

  MBEDTLS_SSL_CONF_SINGLE_UECC_GRP_ID

that indicatesthe TinyCrypt group identifier of the single curve
to use (must be Secp256r1) if MBEDTLS_SSL_CONF_SINGLE_CURVE
and MBEDTLS_USE_TINYCRYPT are set.
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index ef5dfcc..7b25ad2 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1423,7 +1423,7 @@
     scripts/config.pl set MBEDTLS_SSL_CONF_RNG rng_wrap
     scripts/config.pl set MBEDTLS_SSL_CONF_SINGLE_EC
     scripts/config.pl set MBEDTLS_SSL_CONF_SINGLE_EC_TLS_ID 23
-    scripts/config.pl set MBEDTLS_SSL_CONF_SINGLE_EC_GRP_ID MBEDTLS_ECP_DP_SECP256R1
+    scripts/config.pl set MBEDTLS_SSL_CONF_SINGLE_UECC_GRP_ID MBEDTLS_UECC_DP_SECP256R1
     scripts/config.pl unset MBEDTLS_ECDH_C
     scripts/config.pl unset MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED
     scripts/config.pl unset MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED