drm/i915/display: Make get_allowed_dc_mask().max_dc set a chain of if and elses

Just following what we do in many other places, DG1 is a exception so
move it to the top instead of add it inside of INTEL_GEN(dev_priv) >= 12.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201111162408.98002-2-jose.souza@intel.com

drivers/gpu/drm/i915/display/intel_display_power.c

@@ -4492,20 +4492,16 @@ static u32 get_allowed_dc_mask(const struct drm_i915_private *dev_priv,
 	int requested_dc;
 	int max_dc;
 
-	if (INTEL_GEN(dev_priv) >= 12) {
-		if (IS_DG1(dev_priv))
-			max_dc = 3;
-		else
-			max_dc = 4;
-	} else if (IS_GEN(dev_priv, 11)) {
+	if (IS_DG1(dev_priv))
+		max_dc = 3;
+	else if (INTEL_GEN(dev_priv) >= 12)
+		max_dc = 4;
+	else if (INTEL_GEN(dev_priv) >= 10 || IS_GEN9_BC(dev_priv))
 		max_dc = 2;
-	} else if (IS_GEN(dev_priv, 10) || IS_GEN9_BC(dev_priv)) {
-		max_dc = 2;
-	} else if (IS_GEN9_LP(dev_priv)) {
+	else if (IS_GEN9_LP(dev_priv))
 		max_dc = 1;
-	} else {
+	else
 		max_dc = 0;
-	}
 
 	/*
 	 * DC9 has a separate HW flow from the rest of the DC states,