Add Support for Partition Backup and Restores

This adds the ability to do system backups and restores using the flag files full_backup and full_restore, as well as the functions backup_mtd_partition and restore_mtd_partition which can be called from a image file.

Before this is merged, https://github.com/tchebb/eureka_buildroot/pull/2 must be merged upstream otherwise these features will not function properly.