bignum_mod: Refactored `mbedtls_mpi_mod_modulus_setup()`

This patch removes the `int_rep` input parameter for modular
setup, aiming to align it with the optred variant.

Test and test-suite helper functions have been updated
accordingly.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index af649a2..69091c3 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -6003,8 +6003,7 @@
             return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
     }
 
-    if (mbedtls_mpi_mod_modulus_setup(N, p, p_limbs,
-                                      MBEDTLS_MPI_MOD_REP_MONTGOMERY)) {
+    if (mbedtls_mpi_mod_modulus_setup(N, p, p_limbs)) {
         return MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     }
     return 0;