drm/msm/sde: add debug dump and panic facility

Add facility to trigger a dump of logs, and optionally trigger
a panic. To be used on detection of unrecoverable error detected
from within the SDE driver.

Change-Id: If1b48b1dcba21d9747cf85a5de027d694ae4a645
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>