selftests/ftrace: Test kprobe-event argument with various bitsize

Improve the kprobe-event with argument types testcase
to test it with various bitsize.
kprobe-event argument can be recorded in given types with
various bitsize (8, 16, 32, 64), thus the type testcase
should test the different bitsize too.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>