Rename test_suite_bignum_mod.data for consistency

Use the same naming convention as bignum and bignum_core now that test
data is generated.

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
diff --git a/tests/suites/test_suite_bignum_mod.data b/tests/suites/test_suite_bignum_mod.misc.data
similarity index 100%
rename from tests/suites/test_suite_bignum_mod.data
rename to tests/suites/test_suite_bignum_mod.misc.data