drm/i915: clear up backlight #define confusion on gen4+

- Regroup definitions for BLC_PWM_CTL so that they're all together and
  and ordered according to the bitfields.

- Add all missing definitions for BLC_PWM_CTL2.

- Use the BLM_ (for backlight modulation) prefix consistently.

- Note that combination mode (i.e. also taking the legacy backlight
  control value from pci config space into account) is gen4 only.

- Move the new registers for PCH-split machines up, they're an almost
  match for the gen4 defitions.  Prefix the special PCH-only bits with
  BLM_PCH_. Also add the pipe C select bit for ivb.

- Rip out the second pair of PCH polarity definitions - they're only
  valid on early (pre-production) ilk silicon.

- Adapt the existing code to use the new definitions. This has the
  nice benefit of killing a magic (1 << 30) left behind be Jesse
  Barnes.

No functional changes in this patch.

Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 5e76031..bad36e0 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6895,9 +6895,9 @@
 	 * IVB has CPU eDP backlight regs too, set things up to let the
 	 * PCH regs control the backlight
 	 */
-	I915_WRITE(BLC_PWM_CPU_CTL2, PWM_ENABLE);
+	I915_WRITE(BLC_PWM_CPU_CTL2, BLM_PWM_ENABLE);
 	I915_WRITE(BLC_PWM_CPU_CTL, 0);
-	I915_WRITE(BLC_PWM_PCH_CTL1, PWM_ENABLE | (1<<30));
+	I915_WRITE(BLC_PWM_PCH_CTL1, BLM_PCH_PWM_ENABLE | BLM_PCH_OVERRIDE_ENABLE);
 }
 
 void intel_modeset_init_hw(struct drm_device *dev)