SPM: Remove remaining SMC interfaces

Also, add a disclaimer to explain that the current implementation of SPM
is a prototype that is going to undergo a lot of rework.

Change-Id: I303c1e61c51d9f286cc599fea565fc9ba5a996bf
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/services/std_svc/spm/README.rst b/services/std_svc/spm/README.rst
new file mode 100644
index 0000000..63406a3
--- /dev/null
+++ b/services/std_svc/spm/README.rst
@@ -0,0 +1,3 @@
+This is a prototype loosely based on the SPCI Alpha and SPRT pre-alpha
+specifications. Any interface / platform API introduced for this is subject to
+change as it evolves.