drm/i915: kill cargo-culted locking from power well code

We may not concurrently change the power wells code. Which
is already guaranteed since modesets aren't concurrent. That
leaves races against setup/teardown/suspend/resume, and for
those we already (try) rather hard not to hit concurrent
modesets.

No debug WARN_ON added since that would require us to grab the
modeset locks in init/suspend code. Which is again just cargo
culting since just grabbing the locks in those paths isn't good
enough, we need the right order of operations, too.

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -4088,8 +4088,6 @@ void intel_init_power_well(struct drm_device *dev)
 	if (!IS_HASWELL(dev))
 		return;
 
-	mutex_lock(&dev->struct_mutex);
-
 	/* For now, we need the power well to be always enabled. */
 	intel_set_power_well(dev, true);
 
@@ -4097,8 +4095,6 @@ void intel_init_power_well(struct drm_device *dev)
 	 * the driver is in charge now. */
 	if (I915_READ(HSW_PWR_WELL_BIOS) & HSW_PWR_WELL_ENABLE)
 		I915_WRITE(HSW_PWR_WELL_BIOS, 0);
-
-	mutex_unlock(&dev->struct_mutex);
 }
 
 /* Set up chip specific power management-related functions */