bl_common: add BL_END macro

Currently, the end address macros are defined per BL, like BL2_END,
BL31_END, BL32_END. They are not handy in the common code shared
between multiple BL stages.

This commit introduces BL_END, which is equivalent to BL{2,31,32}_END,
and will be useful for the BL-common code.

Change-Id: I3c39bf6096d99ce920a5b9fa21c0f65456fbfe8a
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

include/common/bl_common.h

 /*
- * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -106,6 +106,7 @@ IMPORT_SYM(uintptr_t, __RODATA_END__,		BL_RO_DATA_END);
 IMPORT_SYM(uintptr_t, __RO_START__,		BL_CODE_BASE);
 IMPORT_SYM(uintptr_t, __RO_END__,		BL_CODE_END);
 #endif
+IMPORT_SYM(uintptr_t, __RW_END__,		BL_END);
 
 #if defined(IMAGE_BL1)
 IMPORT_SYM(uintptr_t, __BL1_ROM_END__,		BL1_ROM_END);