Add output size parameter to signature functions

The functions mbedtls_pk_sign(), mbedtls_pk_sign_restartable(),
mbedtls_ecdsa_write_signature() and mbedtls_ecdsa_write_signature_restartable()
now take an extra parameter indicating the size of the output buffer for the
signature.

No change to RSA because for RSA, the output size is trivial to calculate.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/pkey/ecdsa.c

@@ -184,7 +184,7 @@ int main( int argc, char *argv[] )
 
     if( ( ret = mbedtls_ecdsa_write_signature( &ctx_sign, MBEDTLS_MD_SHA256,
                                        hash, sizeof( hash ),
-                                       sig, &sig_len,
+                                       sig, sizeof( sig ), &sig_len,
                                        mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
     {
         mbedtls_printf( " failed\n  ! mbedtls_ecdsa_write_signature returned %d\n", ret );