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/services/std_svc/std_svc_setup.c b/services/std_svc/std_svc_setup.c
index 1d80fa3..1219b34 100644
--- a/services/std_svc/std_svc_setup.c
+++ b/services/std_svc/std_svc_setup.c
@@ -45,7 +45,7 @@
 		ret = 1;
 	}
 
-#if ENABLE_SPM
+#if ENABLE_SPM || SPM_MM
 	if (spm_setup() != 0) {
 		ret = 1;
 	}
@@ -103,7 +103,7 @@
 		SMC_RET1(handle, ret);
 	}
 
-#if ENABLE_SPM && SPM_MM
+#if SPM_MM
 	/*
 	 * Dispatch SPM calls to SPM SMC handler and return its return
 	 * value