Tegra210: support for cluster idle from the CPU

Tegra210: support for cluster idle from the CPU

This patch adds support to enter/exit to/from cluster idle power
state on Tegra210 platforms that do not load BPMP firmware.

The CPU initates the cluster idle sequence on the last standing
CPU, by following these steps:

Entry
-----
* stop other CPUs from waking up
* program the PWM pinmux to tristate for OVR PMIC
* program the flow controller to enter CC6 state
* skip L1 $ flush during cluster power down, as L2 $ is inclusive
  of L1 $ on Cortex-A57 CPUs

Exit
----
* program the PWM pinmux to un-tristate for OVR PMIC
* allow other CPUs to wake up

This patch also makes sure that cluster idle state entry is not
enabled until CL-DVFS is ready.

Change-Id: I54cf31bf72b4a09d9bf9d2baaed6ee5a963c7808
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>