cpuidle: cpuidle-cps: add MIPS CPS cpuidle driver

This patch adds a cpuidle driver for systems based around the MIPS
Coherent Processing System (CPS) architecture. It supports four idle
states:

  - The standard MIPS wait instruction.

  - The non-coherent wait, clock gated & power gated states exposed by
    the recently added pm-cps layer.

The pm-cps layer is used to enter all the deep idle states. Since cores
in the clock or power gated states cannot service interrupts, the
gic_send_ipi_single function is modified to send a power up command for
the appropriate core to the CPC in cases where the target CPU has marked
itself potentially incoherent.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index f04e25f..1b96fb9 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -35,6 +35,11 @@
 source "drivers/cpuidle/Kconfig.arm"
 endmenu
 
+menu "MIPS CPU Idle Drivers"
+depends on MIPS
+source "drivers/cpuidle/Kconfig.mips"
+endmenu
+
 menu "POWERPC CPU Idle Drivers"
 depends on PPC
 source "drivers/cpuidle/Kconfig.powerpc"