overlay: parse tracepoints from sysfs to figure out fields' location

With changes going to drm-tip, the tracepoints field locations are
going to change. This change introduces a tracepoint parser (using a
peg parser) which lets us figure out field positions on the fly.

v2: Fix automake build (Lionel)

v3: Make overlay build conditional on peg (Petri)
    Make wait_end callback more readable (Chris)
    Drop tracepoint_id(), instead parsing from format file (Lionel)

v4: Fix existing configure.ac issue with overlay build (Petri)

v5: Silence unused function (Lionel)

v6: Fix missing double quote in v4 (Lionel)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
For the build system changes:
Acked-by: Petri Latvala <petri.latvala@intel.com>