drm/i915: don't run hsw power well code on !hsw

Dumps annoying noise into the dmesg:

[drm:intel_set_power_well] *ERROR* Timeout enabling power well
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -4053,6 +4053,9 @@ void intel_set_power_well(struct drm_device *dev, bool enable)
 	bool is_enabled, enable_requested;
 	uint32_t tmp;
 
+	if (!IS_HASWELL(dev))
+		return;
+
 	tmp = I915_READ(HSW_PWR_WELL_DRIVER);
 	is_enabled = tmp & HSW_PWR_WELL_STATE;
 	enable_requested = tmp & HSW_PWR_WELL_ENABLE;