davinci: add CPU idle driver

The patch adds support for DaVinci cpu idle driver.

Two idle states are defined:
1. Wait for interrupt
2. Wait for interrupt and DDR self-refresh (or power down)

Some DaVinci SoCs support putting DDR in self-refresh (eg Dm644x, DM6467)
while others support putting DDR in self-refresh and power down (eg DM35x,
DA8xx).

Putting DDR (or mDDR) in power down saves more power than self-refresh.

The patch has been tested on DA850/OMAP-L138 EVM.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
diff --git a/arch/arm/mach-davinci/Makefile b/arch/arm/mach-davinci/Makefile
index be629c5..5eae1a9 100644
--- a/arch/arm/mach-davinci/Makefile
+++ b/arch/arm/mach-davinci/Makefile
@@ -32,3 +32,4 @@
 
 # Power Management
 obj-$(CONFIG_CPU_FREQ)			+= cpufreq.o
+obj-$(CONFIG_CPU_IDLE)			+= cpuidle.o