simpleperf: add shortcut for creating kprobe events.

When using a kprobe event without any arguments, a --kprobe option
isn't needed. For example, when "-e kprobes:do_sys_open" is used
without --kprobe, a default kprobe event is created at the entry
of do_sys_open().

Bug: 160630060
Test: run simpleperf_unit_test.
Change-Id: I62f5616c423ecb104d64a425fbd52e38e57e993e
6 files changed