Bignum tests: make args use input_style

Before arg_ attributes were the arguments as they were defined in the
python script. Turning these into properties and having them take the
form respect the style set in input_style makes the class easier to use
and more consistent.

This change makes the hex_ properties redundant and therefore they are
removed.

There are no semantic changes to the generated test cases. (The order
of appearance of 64 and 32 bit mpi_core_add_and_add_if test cases has
changed.)

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/scripts/mbedtls_dev/bignum_mod_raw.py b/scripts/mbedtls_dev/bignum_mod_raw.py
index b330c49..e2d8cd6 100644
--- a/scripts/mbedtls_dev/bignum_mod_raw.py
+++ b/scripts/mbedtls_dev/bignum_mod_raw.py
@@ -114,8 +114,8 @@
         return [self.hex_x]
 
     def arguments(self) -> List[str]:
-        return [bignum_common.quote_str(n) for n in [self.hex_n,
-                                                     self.hex_a,
+        return [bignum_common.quote_str(n) for n in [self.arg_n,
+                                                     self.arg_a,
                                                      self.hex_x]]
 
     def description(self) -> str: