KVM: selftests: Verify that KVM returns the configured APIC cycle length

KVM: selftests: Verify that KVM returns the configured APIC cycle length

Add checks in the APIC bus clock test to verify that querying
KVM_CAP_X86_APIC_BUS_CYCLES_NS on the VM after changing the frequency
returns the VM's actual APIC cycle length, not KVM's default.  For
giggles, verify that KVM still returns its default frequency for the
system-scoped check.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260522173526.3539407-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>