msm: sde: Adding SW overhead statistic for SDE rotator

Enabling SW overhead statistic collection for SDE rotator. SW overhead
is defined as time between buffer queueing and HW flush.

CRs-Fixed: 1054205
Change-Id: I7f09dafa8c2d0f1940c76913ae842835059122f4
Signed-off-by: Benjamin Chan <bkchan@codeaurora.org>