refactor(spm_mm): reorganize secure partition manager code

In preparation for adding the EL3 SPMC configuration as defined in
the FF-A specification, restructure the existing SPM_MM code.

With this restructuring of the code, the 'spm_mm' directory is
renamed as 'spm' and the code inside has been split into two
sub-directories named 'common' and 'spm_mm'. The code in 'spm_mm'
directory contains the code that implements the MM interface.
In subsequent patches, the 'spmc' directory will be introduced
under the 'spm' directory providing the code that implements
the 'FF-A' interface.

Currently the common functionality for S-EL1 partitions is
limited to assembler functions to enter and exit an SP
synchronously.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: I37739b9b53bc68e151ab5c1c0c6a15b3ee362241
diff --git a/services/std_svc/spm/common/spm.mk b/services/std_svc/spm/common/spm.mk
new file mode 100644
index 0000000..9aa96be
--- /dev/null
+++ b/services/std_svc/spm/common/spm.mk
@@ -0,0 +1,17 @@
+#
+# Copyright (c) 2022, ARM Limited and Contributors. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+ifneq (${ARCH},aarch64)
+        $(error "Error: SPM is only supported on aarch64.")
+endif
+
+INCLUDES	+=	-Iservices/std_svc/spm/common/include
+
+SPM_SOURCES	:=	$(addprefix services/std_svc/spm/common/,\
+			${ARCH}/spm_helpers.S)
+
+# Let the top-level Makefile know that we intend to include a BL32 image
+NEED_BL32		:=	yes