perf/core: Merge struct pmu::pmu_disable_count into struct perf_cpu_pmu_context::pmu_disable_count

Because it makes no sense to have two per-cpu allocations per pmu.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20241104135518.518730578@infradead.org