Add Djinn. (#17382)

* Add Djinn.

* Review comments.

* Further cleanup.

keyboards/tzarc/djinn/graphics/theme_djinn_default.h

@@ -0,0 +1,19 @@
+// Copyright 2018-2022 Nick Brassel (@tzarc)
+// SPDX-License-Identifier: GPL-2.0-or-later
+#pragma once
+
+//----------------------------------------------------------
+// Sync
+
+#pragma pack(push)
+#pragma pack(1)
+typedef struct theme_runtime_config {
+    uint32_t scan_rate;
+} theme_runtime_config;
+#pragma pack(pop)
+
+extern theme_runtime_config theme_state;
+
+void theme_init(void);
+void theme_state_update(void);
+void theme_state_sync(void);