KVM: x86: Init vcpu->arch.perf_capabilities in common x86 code

Initialize vcpu->arch.perf_capabilities in x86's kvm_arch_vcpu_create()
instead of deferring initialization to vendor code.  For better or worse,
common x86 handles reads and writes to the MSR, and so common x86 should
also handle initializing the MSR.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221006000314.73240-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>