adding trace-cmd's plugins to perf

[David Ahern <dsahern@gmail.com>]

Right now perf script cannot process kvm tracepoints:

perf record -e kvm:* -p 6446 -- sleep 5

perf script
  Warning: Error: expected type 4 but read 7
  Warning: Error: expected type 5 but read 0
  Warning: failed to read event print fmt for kvm_apic
  Warning: Error: expected type 4 but read 7
  Warning: Error: expected type 5 but read 0
  Warning: failed to read event print fmt for kvm_inj_exception
  Fatal: bad op token {

trace-cmd can parse the events through the kvm plugin.

As I understand it trace-cmd and perf have a lot of similar code, so I
would expect to be able to add the plugin capability to perf somewhat
easily. However, that does not seem to be the right thing to do (copying
yet more code between the two).

Before I invest a lot of time on this path I figured I should ask what
the intentions (roadmap seems to be too formal a word ;-)) are about
merging common code between the two commands. Also, trace-cmd and perf
are in separate repositories so a shared lib is going to inconvenience
one of the two.

Thanks,
David