mpi:ec: Avoid use mpi_const.
* mpi/ec.c (_gcry_mpi_ec_mul_point): Use mpi_mul_ui. (_gcry_mpi_ec_curve_point): Use mpi_mul_ui and mpi_add_ui. Don't use mpi_const. * tests/t-mpi-point.c (point_on_curve): Add Curve25519.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>