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/programs/ssl/query_config.c b/programs/ssl/query_config.c
index c179419..dd50514 100644
--- a/programs/ssl/query_config.c
+++ b/programs/ssl/query_config.c
@@ -2866,6 +2866,14 @@
     }
 #endif /* MBEDTLS_SSL_CONF_SINGLE_EC_GRP_ID */
 
+#if defined(MBEDTLS_SSL_CONF_SINGLE_UECC_GRP_ID)
+    if( strcmp( "MBEDTLS_SSL_CONF_SINGLE_UECC_GRP_ID", config ) == 0 )
+    {
+        MACRO_EXPANSION_TO_STR( MBEDTLS_SSL_CONF_SINGLE_UECC_GRP_ID );
+        return( 0 );
+    }
+#endif /* MBEDTLS_SSL_CONF_SINGLE_UECC_GRP_ID */
+
 #if defined(MBEDTLS_SSL_CONF_SINGLE_SIG_HASH)
     if( strcmp( "MBEDTLS_SSL_CONF_SINGLE_SIG_HASH", config ) == 0 )
     {