drm/msm: Convert shrinker msgs to tracepoints

This reduces the spam in dmesg when we start hitting the shrinker, and
replaces it with something we can put on a timeline while profiling or
debugging system issues.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>