drm/i915: Move hotplug inversion logic into separate helper

Use *_hpd_invert() helpers whenever possible to isolate logic specific
to hotplug inversion from common HPD setup logic to improve readability
and maintainability of the source code.

While we only define dg1_hpd_invert() here, future platforms are likely
to have different hotplug inversion needs, thus it makes sense grouping
different implementations under a common suffix.

v2: Fix coding style and prefer to use small *_hdp_invert() helpers
    instead of a generic one.

CC: Jani Nikula <jani.nikula@linux.intel.com>
CC: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220922164949.163985-1-gustavo.sousa@intel.com

drivers/gpu/drm/i915/i915_irq.c

@@ -3411,17 +3411,18 @@ static u32 gen11_hotplug_enables(struct drm_i915_private *i915,
 	}
 }
 
-static void dg1_hpd_irq_setup(struct drm_i915_private *dev_priv)
+static void dg1_hpd_invert(struct drm_i915_private *i915)
 {
-	u32 val;
-
-	val = intel_uncore_read(&dev_priv->uncore, SOUTH_CHICKEN1);
-	val |= (INVERT_DDIA_HPD |
-		INVERT_DDIB_HPD |
-		INVERT_DDIC_HPD |
-		INVERT_DDID_HPD);
-	intel_uncore_write(&dev_priv->uncore, SOUTH_CHICKEN1, val);
+	u32 val = (INVERT_DDIA_HPD |
+		   INVERT_DDIB_HPD |
+		   INVERT_DDIC_HPD |
+		   INVERT_DDID_HPD);
+	intel_uncore_rmw(&i915->uncore, SOUTH_CHICKEN1, 0, val);
+}
 
+static void dg1_hpd_irq_setup(struct drm_i915_private *dev_priv)
+{
+	dg1_hpd_invert(dev_priv);
 	icp_hpd_irq_setup(dev_priv);
 }