ecc: Make _gcry_mpi_ec_mul_point friendly to X25519 computation.
* mpi/ec.c (_gcry_mpi_ec_mul_point): Support scalar input as an opaque MPI in little-endian native format. * cipher/ecc-ecdh.c (_gcry_ecc_mul_point): Use an opaque scalar.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>