KVM: x86: Remove unused "flags" of kvm_pv_kick_cpu_op()

The "unsigned long flags" parameter of  kvm_pv_kick_cpu_op() is not used,
so remove it. No functional change intended.

Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
Message-Id: <20220125095909.38122-20-cloudliang@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>