KVM: PPC: Book3S PR: Add emulation for tabort. in privileged state

Currently privileged-state guest will be run with TM disabled.

Although the privileged-state guest cannot initiate a new transaction,
it can use tabort to terminate its problem state's transaction.
So it is still necessary to emulate tabort. for privileged-state guest.

Tested with:
https://github.com/justdoitqd/publicFiles/blob/master/test_tabort.c

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