serrano-common: Set SSR level

Control SSR level from sysfs and set to independent reset to allow a
crashed component, ie modem, to reset itself without taking the system
down.

Requires http://review.cyanogenmod.org/#/c/66317/

Change-Id: Ide411656d71b5bae35e3cb86cc72371fb301e1a2
Merge branch 'cm-11.0' into kk_mkt