build(amu): introduce `amu.mk`

This change introduces the `amu.mk` Makefile, used to remove the need
to manually include AMU sources into the various build images.
Makefiles requiring the list of AMU sources are expected to include
this file and use `${AMU_SOURCES}` to retrieve them.

Change-Id: I3d174033ecdce6439a110d776f0c064c67abcfe0
Signed-off-by: Chris Kay <chris.kay@arm.com>

bl31/bl31.mk

@@ -22,6 +22,7 @@ ifeq (${SPM_MM},1)
   endif
 endif
 
+include lib/extensions/amu/amu.mk
 include lib/psci/psci_lib.mk
 
 BL31_SOURCES		+=	bl31/bl31_main.c				\
@@ -78,8 +79,7 @@ BL31_SOURCES		+=	lib/extensions/spe/spe.c
 endif
 
 ifeq (${ENABLE_AMU},1)
-BL31_SOURCES		+=	lib/extensions/amu/aarch64/amu.c		\
-				lib/extensions/amu/aarch64/amu_helpers.S
+BL31_SOURCES		+=	${AMU_SOURCES}
 endif
 
 ifeq (${ENABLE_SVE_FOR_NS},1)

bl32/sp_min/sp_min.mk

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2016-2020, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2016-2021, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -8,6 +8,7 @@ ifneq (${ARCH}, aarch32)
 	$(error SP_MIN is only supported on AArch32 platforms)
 endif
 
+include lib/extensions/amu/amu.mk
 include lib/psci/psci_lib.mk
 
 INCLUDES		+=	-Iinclude/bl32/sp_min
@@ -27,9 +28,8 @@ ifeq (${ENABLE_PMF}, 1)
 BL32_SOURCES		+=	lib/pmf/pmf_main.c
 endif
 
-ifeq (${ENABLE_AMU}, 1)
-BL32_SOURCES		+=	lib/extensions/amu/aarch32/amu.c\
-				lib/extensions/amu/aarch32/amu_helpers.S
+ifeq (${ENABLE_AMU},1)
+BL32_SOURCES		+=	${AMU_SOURCES}
 endif
 
 ifeq (${WORKAROUND_CVE_2017_5715},1)

lib/extensions/amu/amu.mk

@@ -0,0 +1,8 @@
+#
+# Copyright (c) 2021, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+AMU_SOURCES	:=	lib/extensions/amu/${ARCH}/amu.c \
+			lib/extensions/amu/${ARCH}/amu_helpers.S