perf machine: Factor out machine__idle_thread()

perf machine: Factor out machine__idle_thread()

Factor out machine__idle_thread() so it can be re-used for guest machines.

A thread is needed to find executable code, even for the guest kernel. To
avoid possible future pid number conflicts, the idle thread can be used.

Signed-off-by: Adrian Hunter <[email protected]>
Acked-by: Andi Kleen <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>