generate_test_keys: use keys from asymmetric_key_data.py

asymmetric_key_data.py already provides EC/RSA key pair values that
are suitable for generate_test_keys.py. So instead of re-generating
the keys using gen_key program, we use those keys.

This commit also:
- extends asymmetric_key_data.py to introduce
RSA bit sizes that are used in test_suite_pk but were missing from
asymmetric_key_data.py.
- updates test_keys.h with new keys.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/scripts/check-python-files.sh b/tests/scripts/check-python-files.sh
index 51e8079..cf1f87a 100755
--- a/tests/scripts/check-python-files.sh
+++ b/tests/scripts/check-python-files.sh
@@ -62,6 +62,7 @@
 
 echo
 echo 'Running mypy ...'
+export MYPYPATH="../../scripts"
 $PYTHON -m mypy scripts/*.py tests/scripts/*.py ||
   ret=1