powerpc/pseries: Select ARCH_RANDOM on pseries

We have a driver for the ARCH_RANDOM hook in rng.c, so we should select
ARCH_RANDOM on pseries.

Without this the build breaks if you turn ARCH_RANDOM off.

This hasn't broken the build because pseries_defconfig doesn't specify a
value for PPC_POWERNV, which is default y, and selects ARCH_RANDOM.

Signed-off-by: Michael Ellerman <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/platforms/pseries/Kconfig

···
 	select PPC_DOORBELL
 	select HAVE_CONTEXT_TRACKING
 	select HOTPLUG_CPU if SMP
+	select ARCH_RANDOM
 	default y
 
 config PPC_SPLPAR