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/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index 9ef35d8..cf316d0 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1373,8 +1373,7 @@
     TEST_EQUAL(limbs_res, limbs_N);
 
     TEST_EQUAL(mbedtls_mpi_mod_modulus_setup(
-                   &m, N, limbs_N,
-                   MBEDTLS_MPI_MOD_REP_OPT_RED), 0);
+                   &m, N, limbs_N), 0);
 
     TEST_EQUAL((*curve_func)(X, limbs_X), 0);