perf pmu: Move *_cpuid_str() weak functions to header.c

perf pmu: Move *_cpuid_str() weak functions to header.c

The weak functions, strcmp_cpuid_str() and get_cpuid_str(), are defined
in pmu.c.

Most of the cpuid related functions, including *_cpuid_str()'s
declaration and platform specific definition, are in header.c/h.

To make the declaration and definition of all cpuid related functions in
a consistent place, move the weak functions to header.c.

There is no functional change.

Suggested-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Link: http://lkml.kernel.org/r/20181121164939.13482-1-kan.liang@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>