drm/i915: remove full registers dump debug

This one reverts 9e3a6d15

.
As reported by http://bugzilla.kernel.org/show_bug.cgi?id=14485,
this dump will cause hang problem on some machine. If something
really needs this kind of full registers dump, that could be done
within intel-gpu-tools.

Cc: Ben Gamari <bgamari.foss@gmail.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>