* src/ec-context.h (mpi_ec_ctx_s): Add field FLAGS.
* mpi/ec.c (ec_p_init): Add arg FLAGS.  Change all callers to pass it.
* cipher/ecc-curves.c (point_from_keyparam): Add arg EC, parse as
 opaque mpi and use eddsa decoding depending on the flag.
(_gcry_mpi_ec_new): Rearrange to parse Q and D after knowing the
curve.