refactor(spm-mm): reorganize secure partition manager shim code

In preparation for adding the support for SEL0 SP in EL3 SPMC,
restructure the existing SPM_MM shim code in a way that allows reuse
of the code for both SPM_MM interface and FF-A EL3 SPMC interface. The
code for changing exception levels is identical for both.

With this restructuring of the code, the shim exception code is moved to
the common sub-directory.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: Iadda9cf73f12b56e6a1d31fc21b5ba5dc355867f
diff --git a/services/std_svc/spm/common/spm.mk b/services/std_svc/spm/common/spm.mk
index 9aa96be..9491240 100644
--- a/services/std_svc/spm/common/spm.mk
+++ b/services/std_svc/spm/common/spm.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2022, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2022-2023, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -10,8 +10,9 @@
 
 INCLUDES	+=	-Iservices/std_svc/spm/common/include
 
-SPM_SOURCES	:=	$(addprefix services/std_svc/spm/common/,\
-			${ARCH}/spm_helpers.S)
+SPM_SOURCES	:=	$(addprefix services/std_svc/spm/common/,	\
+			${ARCH}/spm_helpers.S				\
+			${ARCH}/spm_shim_exceptions.S)
 
 # Let the top-level Makefile know that we intend to include a BL32 image
 NEED_BL32		:=	yes