i915: when kgdb is active display compression should be off

If the HW compression is left on, the call backs from the HW will
crash the kernel.  The only time this code is called is when kernel
mode setting is in use with kgdb and the kdb shell.

The atomic display pipe handler callback will reset everything when
kgdb restores kernel to the run state.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
CC: David Airlie <airlied@linux.ie>