selftests/livepatch: Add functions.sh to TEST_PROGS_EXTENDED

Add functions.sh to TEST_PROGS_EXTENDED so that it is installed along
with the rest of the selftests and they can be run.

Originally-by: Shuah Khan <shuah@kernel.org>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>