msm: mdss: debugfs: xlog: display kernel panic cleanup

Cleanup the kernel panic within the display driver to
dump mdp registers before driver panics and remove
unnecessary panic during underrun interrupt.

Change-Id: Ia8cb125b2836096b4179463cb4d4e6d1bd6cd804
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>