KVM: PPC: Book3S PR: Add emulation for treclaim.

This patch adds support for "treclaim." emulation when PR KVM guest
executes treclaim. and traps to host.

We will firstly do treclaim. and save TM checkpoint. Then it is
necessary to update vcpu current reg content with checkpointed vals.
When rfid into guest again, those vcpu current reg content (now the
checkpoint vals) will be loaded into regs.

Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>