msm: kgsl: Clean up the snapshot code

Remove deprecated and crufty code.  Add a kgsl_snapshot instance
to maintain the snapshot state. Document functions better. Move
kgsl_snapshot_add_section to the .c code and make it not inline
(it gets used too much).

Change-Id: Ic0dedbad926e9c06d97c3b895d7bae590e971b04
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>