SNB (and IVB too I suppose) starts to misbehave if the GPU gets stuck
in an infinite batch buffer loop. The GPU apparently hogs something
critical and CPUs start to lose interrupts and whatnot. We can keep
the system limping along by unmasking some interrupts in
GEN6_PMINTRMSK. The EI up interrupt has been previously chosen for
that task, so let's never mask it.

v2: s/gen6_rps_pm_mask/gen6_sanitize_rps_pm_mask/ (Chris)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93122Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1464014568-4529-1-git-send-email-ville.syrjala@linux.intel.com
Cc: stable@vger.kernel.org
(cherry picked from commit 12c100bf)
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>