perf/x86/intel: Factor out intel_pmu_check_extra_regs

Each Hybrid PMU has to check and update its own extra registers before
registration.

The intel_pmu_check_extra_regs will be reused later to check the extra
registers of each hybrid PMU.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Link: https://lkml.kernel.org/r/1618237865-33448-14-git-send-email-kan.liang@linux.intel.com