disp: msm: sde: log pp-line count in event logs

Log ping-pong current line count during ctl-start
and rd-ptr interrupt. This will help in debugging
ping-pong timeout issues.

Change-Id: I58185330fe9e8a64f48d6da60c974b23a9e68b44
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>