At init time, check the powerdomains lookup is successful otherwise
exit the cpuidle driver init function with -ENODEV like what is done for the
omap3 cpuidle driver.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Jean Pihet <j-pihet@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>