spm-mm: Refactor secure_partition.h and its contents

Before adding any new SPM-related components we should first do
some cleanup around the existing SPM-MM implementation. The aim
is to make sure that any SPM-MM components have names that clearly
indicate that they are MM-related. Otherwise, when adding new SPM
code, it could quickly become confusing as it would be unclear to
which component the code belongs.

The secure_partition.h header is a clear example of this, as the
name is generic so it could easily apply to any SPM-related code,
when it is in fact SPM-MM specific.

This patch renames the file and the two structures defined within
it, and then modifies any references in files that use the header.

Change-Id: I44bd95fab774c358178b3e81262a16da500fda26
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/plat/arm/common/arm_common.c b/plat/arm/common/arm_common.c
index bc0cf9a..03d842a 100644
--- a/plat/arm/common/arm_common.c
+++ b/plat/arm/common/arm_common.c
@@ -16,7 +16,7 @@
 #include <lib/xlat_tables/xlat_tables_compat.h>
 #include <plat/arm/common/plat_arm.h>
 #include <plat/common/platform.h>
-#include <services/secure_partition.h>
+#include <services/spm_mm_partition.h>
 
 /* Weak definitions may be overridden in specific ARM standard platform */
 #pragma weak plat_get_ns_image_entrypoint