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_private.h b/plat/mediatek/mt8188/include/plat_private.h
new file mode 100644
index 0000000..4d4ac85
--- /dev/null
+++ b/plat/mediatek/mt8188/include/plat_private.h
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2022, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef PLAT_PRIVATE_H
+#define PLAT_PRIVATE_H
+
+/*******************************************************************************
+ * Function and variable prototypes
+ ******************************************************************************/
+void plat_configure_mmu_el3(uintptr_t total_base,
+			    uintptr_t total_size,
+			    uintptr_t ro_start,
+			    uintptr_t ro_limit);
+
+#endif /* PLAT_PRIVATE_H */