drm/i915/dc3co: Add description of how it works

Add a basic description about how DC3CO works to help people not
familiar with it.

While at it, I also improved the delayed work handle and function
names and removed a debug message that is ambiguous and not much
useful, no changes in behavior here.

Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200205214945.131012-1-jose.souza@intel.com
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 3452926..da509d9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -504,7 +504,7 @@ struct i915_psr {
 	u16 su_x_granularity;
 	bool dc3co_enabled;
 	u32 dc3co_exit_delay;
-	struct delayed_work idle_work;
+	struct delayed_work dc3co_work;
 	bool initially_probed;
 };