cpuidle: Default y on powerpc pSeries

We moved all our pSeries idle loops to the cpu idle framework
so we really want it to come up by default.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/cpuidle/Kconfig

 
 config CPU_IDLE
 	bool "CPU idle PM support"
-	default ACPI
+	default y if ACPI || PPC_PSERIES
 	help
 	  CPU idle is a generic framework for supporting software-controlled
 	  idle processor power management.  It includes modular cross-platform