msm: mdss: Start ESD BTA status check after unblank done

BTA status check currently is invoked as soon as ESD thread
starts. In some cases, this BTA status check might fail as
unblank is not yet performed and panel is not on. Hence
delay BTA status check start till unblank is completed.

Change-Id: Ic752866cc679438fb2ccffede660c29e9597d01e
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>