SMT thread status register (PPR) is used to set thread priority. This patch
enables PPR save/restore feature (CPU_FTR_HAS_PPR) on POWER7 and POWER8 systems.
Signed-off-by: Haren Myneni <haren@us.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>