KVM: Hoist kvm_create_lapic() into kvm_vcpu_init()

Move kvm_create_lapic() into kvm_vcpu_init(), rather than having svm
and vmx do it.  And make it return the error rather than a fairly
random -ENOMEM.

This also solves the problem that neither svm.c nor vmx.c actually
handles the error path properly.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>