KVM: SVM: allocate AVIC data structures based on kvm_amd module parameter

Even if APICv is disabled at startup, the backing page and ir_list need
to be initialized in case they are needed later.  The only case in
which this can be skipped is for userspace irqchip, and that must be
done because avic_init_backing_page dereferences vcpu->arch.apic
(which is NULL for userspace irqchip).

Tested-by:  <rmuncrief@humanavance.com>
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=206579


Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>