Return and propagate UECC_FAULT_DETECTED

This commit first changes the return convention of EccPoint_mult_safer() so
that it properly reports when faults are detected. Then all functions that
call it need to be changed to (1) follow the same return convention and (2)
properly propagate UECC_FAULT_DETECTED when it occurs.

Here's the reverse call graph from EccPoint_mult_safer() to the rest of the
library (where return values are translated to the MBEDTLS_ERR_ space) and test
functions (where expected return values are asserted explicitly).

EccPoint_mult_safer()
    EccPoint_compute_public_key()
        uECC_compute_public_key()
            pkparse.c
            tests/suites/test_suite_pkparse.function
        uECC_make_key_with_d()
        uECC_make_key()
            ssl_cli.c
            ssl_srv.c
            tests/suites/test_suite_pk.function
            tests/suites/test_suite_tinycrypt.function
    uECC_shared_secret()
        ssl_tls.c
        tests/suites/test_suite_tinycrypt.function
    uECC_sign_with_k()
        uECC_sign()
            pk.c
            tests/suites/test_suite_tinycrypt.function

Note: in uECC_sign_with_k() a test for uECC_vli_isZero(p) is suppressed
because it is redundant with a more thorough test (point validity) done at the
end of EccPoint_mult_safer(). This redundancy was introduced in a previous
commit but not noticed earlier.
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 43ca2ca..1ef8f94 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3410,6 +3410,7 @@
 
 #if defined(MBEDTLS_USE_TINYCRYPT)
         {
+            int ret;
             static const unsigned char ecdh_param_hdr[] = {
                 MBEDTLS_SSL_EC_TLS_NAMED_CURVE,
                 0  /* high bits of secp256r1 TLS ID  */,
@@ -3426,12 +3427,12 @@
                     ecdh_param_hdr, sizeof( ecdh_param_hdr ) );
             ssl->out_msglen += sizeof( ecdh_param_hdr );
 
-            if( !uECC_make_key( &ssl->out_msg[ ssl->out_msglen ],
-                                ssl->handshake->ecdh_privkey ) )
-            {
-                MBEDTLS_SSL_DEBUG_MSG( 1, ( "Key creation failed" ) );
-                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
-            }
+            ret = uECC_make_key( &ssl->out_msg[ ssl->out_msglen ],
+                                 ssl->handshake->ecdh_privkey );
+            if( ret == UECC_FAULT_DETECTED )
+                return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
+            if( ret != UECC_SUCCESS )
+                return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
 
             ssl->out_msglen += 2*NUM_ECC_BYTES;
         }