KVM: x86: Fix PV IPIs for 32-bit KVM host

commit 1ed199a41c70ad7bfaee8b14f78e791fcf43b278 upstream.

The recognition of the KVM_HC_SEND_IPI hypercall was unintentionally
wrapped in "#ifdef CONFIG_X86_64", causing 32-bit KVM hosts to reject
any and all PV IPI requests despite advertising the feature.  This
results in all KVM paravirtualized guests hanging during SMP boot due
to IPIs never being delivered.

Fixes: 4180bf1b ("KVM: X86: Implement "send IPI" hypercall")
Cc: stable@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>