powerpc/pseries: Enable PRRN handling

The Linux kernel and platform firmware negotiate their mutual support
of the PRRN option via the ibm,client-architecture-support interface.
This patch simply sets the appropriate fields in the client architecture
vector to indicate Linux support for PRRN and will allow the firmware to
report PRRN events via the RTAS event-scan mechanism.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>