x86/perf/intel/rapl: Make the Intel RAPL PMU driver modular

By default, the RAPL driver will be built into the kernel. If it is
configured as a module, the supported CPU model can be auto loaded.

Also clean up the code of rapl_pmu_init().

Based-on-a-patch-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/1458372050-2420-2-git-send-email-kan.liang@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>