Hibernate: generate and compare digest in compress path

This patch generate digest of snapshot in save_image_lzo and compare
digest in load_image_lzo. The performance better then uncompress path
but it's still hurt the performance of load_image_lzo, almost 5 times of
non-hash.
This patch will need adapt to RSA signature generation/verification
mechanism, and also add CONFIG and force parameter like kernel
module sign facility.

Signed-off-by: Lee, Chun-Yi <jlee@suse.com>