perf tools: Allow r0x<HEX> event syntax

Add support to specify raw event with 'r0<HEX>' syntax within pmu term
syntax like:

  -e cpu/r0xdead/

It will be used to specify raw events in cases where they conflict with
real pmu terms, like 'read', which is valid raw event syntax, but also a
possible pmu term name as reported by Jin Yao.

Reported-by: Jin Yao <yao.jin@linux.intel.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20200725121959.1181869-1-jolsa@kernel.org


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