ARM: OMAP4: PM: Add CPUX OFF mode support

This patch adds the CPU0 and CPU1 off mode support. CPUX close switch
retention (CSWR) is not supported by hardware design.

The CPUx OFF mode isn't supported on OMAP4430 ES1.0

CPUx sleep code is common for hotplug, suspend and CPUilde.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Vishwanath BS <vishwanath.bs@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>