KVM: x86: Track supported PERF_CAPABILITIES in kvm_caps

Track KVM's supported PERF_CAPABILITIES in kvm_caps instead of computing
the supported capabilities on the fly every time.  Using kvm_caps will
also allow for future cleanups as the kvm_caps values can be used
directly in common x86 code.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Acked-by: Like Xu <likexu@tencent.com>
Message-Id: <20221006000314.73240-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>