perf intel-pt: Support decoding of guest kernel

perf intel-pt: Support decoding of guest kernel

The guest kernel can be found from any guest thread belonging to the guest
machine. The guest machine is associated with the current host process pid.
An idle thread (pid=tid=0) is created as a vehicle from which to find the
guest kernel map.

Decoding guest user space is not supported.

Synthesized samples just need the cpumode set for the guest.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210218095801.19576-8-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>