KVM: x86: Eliminate log spam from limited APIC timer periods

SAP's vSMP MemoryONE continuously requests a local APIC timer period
less than 500 us, resulting in the following kernel log spam:

  kvm: vcpu 15: requested 70240 ns lapic timer period limited to 500000 ns
  kvm: vcpu 19: requested 52848 ns lapic timer period limited to 500000 ns
  kvm: vcpu 15: requested 70256 ns lapic timer period limited to 500000 ns
  kvm: vcpu 9: requested 70256 ns lapic timer period limited to 500000 ns
  kvm: vcpu 9: requested 70208 ns lapic timer period limited to 500000 ns
  kvm: vcpu 9: requested 387520 ns lapic timer period limited to 500000 ns
  kvm: vcpu 9: requested 70160 ns lapic timer period limited to 500000 ns
  kvm: vcpu 66: requested 205744 ns lapic timer period limited to 500000 ns
  kvm: vcpu 9: requested 70224 ns lapic timer period limited to 500000 ns
  kvm: vcpu 9: requested 70256 ns lapic timer period limited to 500000 ns
  limit_periodic_timer_frequency: 7569 callbacks suppressed
  ...

To eliminate this spam, change the pr_info_ratelimited() in
limit_periodic_timer_frequency() to pr_info_once().

Reported-by: James Houghton <jthoughton@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Message-ID: <20240724190640.2449291-1-jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>