KVM: Move vcpu->run page allocation out of kvm_vcpu_init()

Open code the allocation and freeing of the vcpu->run page in
kvm_vm_ioctl_create_vcpu() and kvm_vcpu_destroy() respectively.  Doing
so allows kvm_vcpu_init() to be a pure init function and eliminates
kvm_vcpu_uninit() entirely.

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