ppc: Add software breakpoint support

This patch allow insert/remove software breakpoint.

When QEMU is not able to handle debug exception then we inject
program exception to guest because for software breakpoint QEMU
uses a ehpriv-1 instruction;
So there cannot be any reason that we are in qemu with exit reason
KVM_EXIT_DEBUG  for guest set debug exception, only possibility is
guest executed ehpriv-1 privilege instruction and that's why we are
injecting program exception.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
[agraf: make deflect comment booke/book3s agnostic]
Signed-off-by: Alexander Graf <agraf@suse.de>
