perf scripting: Add scripting_context__update()

Move scripting_context update to a separate function and add
the arguments of ->process_event() to it.

This prepares the way for adding more methods to the perf_trace_context
module, by providing the context information that they will need.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210530192308.7382-4-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>