drm/i915: restrict kernel address leak in debugfs

commit 2563a4524febe8f4a98e717e02436d1aaf672aa2 upstream.

Masks kernel address info-leak in object dumps with the %pK suffix,
so they cannot be used to target kernel memory corruption attacks if
the kptr_restrict sysctl is set.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[bwh: Backported to 3.2: the rest of the format string is different]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>