drm/i915/ipc: register debugfs only if IPC available

It looks like trying to enable IPC via debugfs on platforms that don't
have IPC resulted in dmesg info message about IPC being enabled, which
is clearly not possible and would not happen.

Seems sensible to register IPC debugfs only on platforms that have IPC.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b18edb4f96c9d2ec728ef04e6f99d161fe5641d1.1662983005.git.jani.nikula@intel.com

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

@@ -3485,9 +3485,6 @@ static int skl_watermark_ipc_status_open(struct inode *inode, struct file *file)
 {
 	struct drm_i915_private *i915 = inode->i_private;
 
-	if (!HAS_IPC(i915))
-		return -ENODEV;
-
 	return single_open(file, skl_watermark_ipc_status_show, i915);
 }
 
@@ -3529,6 +3526,9 @@ void skl_watermark_ipc_debugfs_register(struct drm_i915_private *i915)
 {
 	struct drm_minor *minor = i915->drm.primary;
 
+	if (!HAS_IPC(i915))
+		return;
+
 	debugfs_create_file("i915_ipc_status", 0644, minor->debugfs_root, i915,
 			    &skl_watermark_ipc_status_fops);
 }