KVM: PPC: debug stub interface parameter defined

This patch defines the interface parameter for KVM_SET_GUEST_DEBUG
ioctl support. Follow up patches will use this for setting up
hardware breakpoints, watchpoints and software breakpoints.

Also kvm_arch_vcpu_ioctl_set_guest_debug() is brought one level below.
This is because I am not sure what is required for book3s. So this ioctl
behaviour will not change for book3s.

Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>