ARM: imx: support arm power off in cpuidle for i.mx6sx
This patch introduces an independent cpuidle driver for
i.MX6SX, and supports arm power off in idle, totally
3 levels of cpuidle are supported as below:
1. ARM WFI;
2. SOC in WAIT mode;
3. SOC in WAIT mode + ARM power off.
ARM power off can save at least 5mW power.
This patch also replaces imx6q_enable_rbc with imx6_enable_rbc.