feat(mt8186): initialize platform for MediaTek MT8186

- Add basic platform setup.
- Add MT8186 documentation at docs/plat/.
- Add generic CPU helper functions.
- Add basic register address.

TEST=build pass
BUG=b:202871018

Change-Id: Id3e2f46a8c3ab2f3e29137e508d4c671e8f4aad5
diff --git a/plat/mediatek/mt8186/include/plat_private.h b/plat/mediatek/mt8186/include/plat_private.h
new file mode 100644
index 0000000..7ef2b85
--- /dev/null
+++ b/plat/mediatek/mt8186/include/plat_private.h
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2021, 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 */