spm-mm: Rename aarch64 assembly files

Change-Id: I2bab67f319758dd033aa689d985227cad796cdea
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/services/std_svc/spm_mm/spm_mm.mk b/services/std_svc/spm_mm/spm_mm.mk
index 1de31a6..656488b 100644
--- a/services/std_svc/spm_mm/spm_mm.mk
+++ b/services/std_svc/spm_mm/spm_mm.mk
@@ -12,8 +12,8 @@
 endif
 
 SPM_SOURCES	:=	$(addprefix services/std_svc/spm_mm/,	\
-			${ARCH}/spm_helpers.S			\
-			${ARCH}/spm_shim_exceptions.S		\
+			${ARCH}/spm_mm_helpers.S			\
+			${ARCH}/spm_mm_shim_exceptions.S		\
 			spm_mm_main.c				\
 			spm_mm_setup.c				\
 			spm_mm_xlat.c)