drm/i915/skl: use ranges for voltage level lookup

Like was done for ICL, let's convert the voltage level lookup to use
frequency ranges rather than individual frequencies. For deciding the
voltage, the individual value doesn't really matter.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190610214847.9865-1-lucas.demarchi@intel.com

drivers/gpu/drm/i915/intel_cdclk.c

@@ -809,20 +809,14 @@ static int skl_calc_cdclk(int min_cdclk, int vco)
 
 static u8 skl_calc_voltage_level(int cdclk)
 {
-	switch (cdclk) {
-	default:
-	case 308571:
-	case 337500:
-		return 0;
-	case 450000:
-	case 432000:
-		return 1;
-	case 540000:
-		return 2;
-	case 617143:
-	case 675000:
+	if (cdclk > 540000)
 		return 3;
-	}
+	else if (cdclk > 450000)
+		return 2;
+	else if (cdclk > 337500)
+		return 1;
+	else
+		return 0;
 }
 
 static void skl_dpll0_update(struct drm_i915_private *dev_priv,