ARM: OMAP4: PM: Add WakeupGen and secure GIC low power support

Add WakeupGen and secure GIC low power support to save and restore
it's registers. WakeupGen Registers are saved to pre-defined SAR RAM layout
and the restore is automatically done by hardware(ROM code) while coming
out of MPUSS OSWR or Device off state. Secure GIC is saved using secure
API and restored by hardware like WakeupGen.

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>