drm/i915: Dont enable CS_PARSER_ERROR interrupts at all

We stopped handling them in

commit aaecdf61
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Nov 4 15:52:22 2014 +0100

    drm/i915: Stop gathering error states for CS error interrupts

but just clearing is apparently not enough: A sufficiently dead gpu
left behind by firmware (*cough* coreboot *cough*) can keep the gpu in
an endless loop of such interrupts, eventually leading to the nmi
firing. And definitely to what looks like a machine hang.

Since we don't even enable these interrupts on gen5+ let's do the same
on earlier platforms.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=93171


Tested-by: Mono <mono-for-kernel-org@donderklumpen.de>
Tested-by:  <info@gluglug.org.uk>
Cc: stable@vger.kernel.org
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>