KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities

KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities

Take a snapshot of the unadulterated PMU capabilities provided by perf so
that KVM can compare guest vPMU capabilities against hardware capabilities
when determining whether or not to intercept PMU MSRs (and RDPMC).

Reviewed-by: Sandipan Das <sandipan.das@amd.com>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Link: https://lore.kernel.org/r/20250806195706.1650976-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>