drm/i915: Allow some leniency in PCU reads

Extend the timeout for pcode reads to 20ms as they should not be
performed along critical paths, and succeeding after a short delay is
better than failing entirely.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/1800
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200504044903.7626-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_sideband.c

@@ -429,7 +429,7 @@ int sandybridge_pcode_read(struct drm_i915_private *i915, u32 mbox,
 
 	mutex_lock(&i915->sb_lock);
 	err = __sandybridge_pcode_rw(i915, mbox, val, val1,
-				     500, 0,
+				     500, 20,
 				     true);
 	mutex_unlock(&i915->sb_lock);