oprofile: Make op_name_from_perf_id() global

Make op_name_from_perf_id() global so that we have a way for each
architecture to construct an oprofile name for op->cpu_type. We need to
remove the argument from the function prototype so that we can hide all
implementation details inside the function.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Robert Richter <robert.richter@amd.com>