KVM: PPC: Book3S PR: Allocate book3s and shadow vcpu after common init

Call kvm_vcpu_init() in kvmppc_core_vcpu_create_pr() prior to allocating
the book3s and shadow_vcpu objects in preparation of moving said call to
common PPC code.  Although kvm_vcpu_init() has an arch callback, the
callback is empty for Book3S PR, i.e. barring unseen black magic, moving
the allocation has no real functional impact.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>