drm/i915: add onoff utility function

Add a common function to return "on" or "off" string based on the
argument, and drop the local versions of it.

This is the onoff version of

commit 42a8ca4cb4a48ddbf40e8edb291425e76bcdc230
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Thu Aug 27 16:23:30 2015 +0300

    drm/i915: add yesno utility function

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452768814-29787-1-git-send-email-jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 9df9e9a..465ca76 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4590,13 +4590,13 @@
 	}
 	if (HAS_RC6p(dev))
 		DRM_DEBUG_KMS("Enabling RC6 states: RC6 %s RC6p %s RC6pp %s\n",
-			      (mode & GEN6_RC_CTL_RC6_ENABLE) ? "on" : "off",
-			      (mode & GEN6_RC_CTL_RC6p_ENABLE) ? "on" : "off",
-			      (mode & GEN6_RC_CTL_RC6pp_ENABLE) ? "on" : "off");
+			      onoff(mode & GEN6_RC_CTL_RC6_ENABLE),
+			      onoff(mode & GEN6_RC_CTL_RC6p_ENABLE),
+			      onoff(mode & GEN6_RC_CTL_RC6pp_ENABLE));
 
 	else
 		DRM_DEBUG_KMS("Enabling RC6 states: RC6 %s\n",
-			      (mode & GEN6_RC_CTL_RC6_ENABLE) ? "on" : "off");
+			      onoff(mode & GEN6_RC_CTL_RC6_ENABLE));
 }
 
 static int sanitize_rc6_option(const struct drm_device *dev, int enable_rc6)
@@ -4774,8 +4774,7 @@
 	/* 3a: Enable RC6 */
 	if (intel_enable_rc6(dev) & INTEL_RC6_ENABLE)
 		rc6_mask = GEN6_RC_CTL_RC6_ENABLE;
-	DRM_INFO("RC6 %s\n", (rc6_mask & GEN6_RC_CTL_RC6_ENABLE) ?
-			"on" : "off");
+	DRM_INFO("RC6 %s\n", onoff(rc6_mask & GEN6_RC_CTL_RC6_ENABLE));
 	/* WaRsUseTimeoutMode */
 	if (IS_SKL_REVID(dev, 0, SKL_REVID_D0) ||
 	    IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {