perf symbols: Add 'intel_idle_ibrs' to the list of idle symbols

perf symbols: Add 'intel_idle_ibrs' to the list of idle symbols

This is a longstanding to do list entry: we need a way to see that a
sample took place while in idle state, as the current way to do it is
to infer that by the name of the functions that in such state have
more samples, IOW: a hack.

Maybe we can do flip a bit in samples that take place inside the
enter/exit idle section in do_idle()?

But till then, add one more :-\

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/ZR66Qgbcltt+zG7F@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>