mpi:ec: Refactor _gcry_mpi_ec_mul_point
* mpi/ec.c (montgomery_mul_point, mpi_ec_mul_point_lli): Factor out from _gcry_mpi_ec_mul_point. (_gcry_mpi_ec_mul_point): Use montgomery_mul_point and mpi_ec_mul_point_lli.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>