OMAP3: PM: SCM context save/restore

Add context save and restore for the System Control Module to suport
off-mode.

ETK and debobs definitions added by Peter De Schrijver.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Peter 'p2' De Schrijver <peter.de-schrijver@nokia.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>