KVM: x86: reset lapic base in kvm_lapic_reset

LAPIC is reset in xAPIC mode and the surrounding code expects that.
KVM never resets after initialization.  This patch is just for sanity.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>