perf, x86: Implement user-space RDPMC support, to allow fast, user-space access to self-monitoring counters

Implement a correct pmu::event_idx for the x86 counter index rules and
set CR4.PCE on CPU_STARTING.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Arun Sharma <asharma@fb.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: http://lkml.kernel.org/n/tip-mwxab34dibqgzk5zywutfnha@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>