ecp_curves: Updated the optimised reduction function pointer.

This patch modifies the `mbedtls_mpi_opt_red_struct` to use an
mpi_uint * pointer and size_t limps arguments.

The methods interacting with this pointer have been updated
accordingly:

- mbedtls_mpi_mod_optred_modulus_setup
- mbedtls_ecp_modulus_setup

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>

library/bignum_mod.c

@@ -166,7 +166,8 @@ int mbedtls_mpi_mod_modulus_setup(mbedtls_mpi_mod_modulus *N,
 int mbedtls_mpi_mod_optred_modulus_setup(mbedtls_mpi_mod_modulus *N,
                                          const mbedtls_mpi_uint *p,
                                          size_t p_limbs,
-                                         int (*modp)(mbedtls_mpi *))
+                                         int (*modp)(mbedtls_mpi_uint *X,
+                                                     size_t X_limbs))
 {
     standard_modulus_setup(N, p, p_limbs, MBEDTLS_MPI_MOD_REP_OPT_RED);
     N->rep.ored.modp = modp;