perf/x86/core: Plumb mediated PMU capability from x86_pmu to x86_pmu_cap

perf/x86/core: Plumb mediated PMU capability from x86_pmu to x86_pmu_cap

Plumb mediated PMU capability to x86_pmu_cap in order to let any kernel
entity such as KVM know that host PMU support mediated PMU mode and has
the implementation.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Link: https://patch.msgid.link/20251206001720.468579-12-seanjc@google.com