selftests/lkdtm: Add UBSAN config

UBSAN_BOUNDS and UBSAN_TRAP depend on UBSAN config option.
merge_config.sh script generates following warnings if parent config
doesn't have UBSAN config already enabled and UBSAN_BOUNDS/UBSAN_TRAP
config options don't get added to the parent config.

Value requested for CONFIG_UBSAN_BOUNDS not in final .config
Requested value:  CONFIG_UBSAN_BOUNDS=y
Actual value:

Value requested for CONFIG_UBSAN_TRAP not in final .config
Requested value:  CONFIG_UBSAN_TRAP=y
Actual value:

Fix this by including UBSAN config.

Fixes: c75be56e ("lkdtm/bugs: Add ARRAY_BOUNDS to selftests")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>