msm: mdss: force display panel status dead

Display panels can be in a bad state which is most likely caused by
ESD shocks. Display s/w has the ability to detect panel state and if
it is bad, s/w reset and recover the panel from that bad state. For
the testability purpose, this change simulates a panel dead state, for
example:

adb shell 'echo 5 > /sys/devices/virtual/graphics/fb0/msm_fb_panel_status'

will simulate a display dead state after 5 detections, which is about
25 seconds if the esd detection feature is enabled with periodic
detections every 5 seconds.

Change-Id: Ia28e80ffcbfe45a59ae65e0e26b558a467b50863
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>