x86/kvm: remove non-x86 stuff from arch/x86/kvm/ioapic.h

The file has been moved to arch/x86 long time ago. Time to get rid of
non-x86 stuff.

Signed-off-by: Juergen Gross <jgross@suse.com>
Message-Id: <20210701154105.23215-3-jgross@suse.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>