Remove dependency between SPM_MM and ENABLE_SPM build flags

There are two different implementations of Secure Partition
management in TF-A. One is based on the "Management Mode" (MM)
design, the other is based on the Secure Partition Client Interface
(SPCI) specification. Currently there is a dependency between their
build flags that shouldn't exist, making further development
harder than it should be. This patch removes that
dependency, making the two flags function independently.

Before: ENABLE_SPM=1 is required for using either implementation.
        By default, the SPCI-based implementation is enabled and
        this is overridden if SPM_MM=1.

After: ENABLE_SPM=1 enables the SPCI-based implementation.
       SPM_MM=1 enables the MM-based implementation.
       The two build flags are mutually exclusive.

Note that the name of the ENABLE_SPM flag remains a bit
ambiguous - this will be improved in a subsequent patch. For this
patch the intention was to leave the name as-is so that it is
easier to track the changes that were made.

Change-Id: I8e64ee545d811c7000f27e8dc8ebb977d670608a
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/plat/socionext/synquacer/sq_bl31_setup.c b/plat/socionext/synquacer/sq_bl31_setup.c
index c78fe91..b864021 100644
--- a/plat/socionext/synquacer/sq_bl31_setup.c
+++ b/plat/socionext/synquacer/sq_bl31_setup.c
@@ -159,7 +159,7 @@
 void bl31_plat_arch_setup(void)
 {
 	static const mmap_region_t secure_partition_mmap[] = {
-#if ENABLE_SPM && SPM_MM
+#if SPM_MM
 		MAP_REGION_FLAT(PLAT_SPM_BUF_BASE,
 				PLAT_SPM_BUF_SIZE,
 				MT_RW_DATA | MT_SECURE),
@@ -173,7 +173,7 @@
 	sq_mmap_setup(BL31_BASE, BL31_SIZE, secure_partition_mmap);
 	enable_mmu_el3(XLAT_TABLE_NC);
 
-#if ENABLE_SPM && SPM_MM
+#if SPM_MM
 	memcpy((void *)SPM_SHIM_EXCEPTIONS_START,
 	       (void *)SPM_SHIM_EXCEPTIONS_LMA,
 	       (uintptr_t)SPM_SHIM_EXCEPTIONS_END -