This patch adds a way to locate a register identifier (PERF_X86_REG_*)
based on its name, e.g., AX.

This will be used by a subsequent patch to improved flexibility of perf
record.
Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1441039273-16260-3-git-send-email-eranian@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>