feat(rme): add ENABLE_RME build option and support for RMM image

The changes include:

- A new build option (ENABLE_RME) to enable FEAT_RME

- New image called RMM. RMM is R-EL2 firmware that manages Realms.
  When building TF-A, a path to RMM image can be specified using
  the "RMM" build flag. If RMM image is not provided, TRP is built
  by default and used as RMM image.

- Support for RMM image in fiptool

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: I017c23ef02e465a5198baafd665a60858ecd1b25
diff --git a/include/bl31/bl31.h b/include/bl31/bl31.h
index 3deb0a5..1d58ef9 100644
--- a/include/bl31/bl31.h
+++ b/include/bl31/bl31.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2021, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -19,6 +19,7 @@
 uint32_t bl31_get_next_image_type(void);
 void bl31_prepare_next_image_entry(void);
 void bl31_register_bl32_init(int32_t (*func)(void));
+void bl31_register_rmm_init(int32_t (*func)(void));
 void bl31_warm_entrypoint(void);
 void bl31_main(void);
 void bl31_lib_init(void);