Add kexec hardboot support for Nexus 7 2013 WIFI/LTE(flo/deb)

This will allow for multirom use. Credit for the patch goes to tasssadar from XDA i only merge to slim.

Change-Id: I7642ce8ee2fc19c6e45e50f93e14b507f24da638
Merge "Add kexec hardboot support for Nexus 7 2013 WIFI/LTE(flo/deb)" into kk4.4