tegra: dc: New trace event for latency measurement

tegra: dc: New trace event for latency measurement

Adds a new trace event to get the timestamp when
the dc gets unblocked on pre_syncpt_fence for a
particular flip.

This (sync_wt_ovr_syncpt_upd) alongwith the
existing trace events (flip_rcvd_syncpt_upd and
scanout_syncpt_upd) help us in measuring latency
from the point we receive a flip, the point at
which the frame is ready for scan-out and the
instant dc actually scans out the same frame.

Reviewed-on: http://git-master/r/729291
(cherry picked from commit f16e6c6344e48081e079348610d05ac80df0e1ad)
Change-Id: Icc007a58f161570b7dab090bcc843cc8065a1bc6
Signed-off-by: Arun Swain <arswain@nvidia.com>
Reviewed-on: http://git-master/r/738658
GVS: Gerrit_Virtual_Submit
Reviewed-by: Mitch Luban <mluban@nvidia.com>