feat(mt8188): initialize platform for MediaTek MT8188

- Add basic platform setup.
- Add MT8188 documentation at docs/plat/.
- Add generic CPU helper functions.
- Add basic register address.
- Add mtk_pm.c in lib/pm

TEST=build pass
BUG=b:236331724

Change-Id: I5f8617c42ffba2c9d3a16f3980cb75fda5624031
diff --git a/plat/mediatek/mt8188/include/plat_helpers.h b/plat/mediatek/mt8188/include/plat_helpers.h
new file mode 100644
index 0000000..eb78623
--- /dev/null
+++ b/plat/mediatek/mt8188/include/plat_helpers.h
@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2022, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef PLAT_HELPERS_H
+#define PLAT_HELPERS_H
+
+unsigned int plat_mediatek_calc_core_pos(u_register_t mpidr);
+
+#endif /* PLAT_HELPERS_H */