KVM: PPC: Book3S PR: Exiting split hack mode needs to fixup both PC and LR

When an OS (currently only classic Mac OS) is running in KVM-PR and makes a
linked jump from code with split hack addressing enabled into code that does
not, LR is not correctly updated and reflects the previously munged PC.

To fix this, this patch undoes the address munge when exiting split
hack mode so that code relying on LR being a proper address will now
execute. This does not affect OS X or other operating systems running
on KVM-PR.

Signed-off-by: Cameron Kaiser <spectre@floodgap.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>