SPM: Allow entering the SP without needing a SMC

It may be needed to enter the Secure Partition through other means than
an MM_COMMUNICATE SMC. This patch enables this behaviour by extracting
the necessary code from mm_communicate() and allowing other parts of the
code to use it.

Change-Id: I59f6638d22d9c9d0baff0984f39d056298a8dc8e
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/services/spm_svc.h b/include/services/spm_svc.h
index 8f872c3..0200992 100644
--- a/include/services/spm_svc.h
+++ b/include/services/spm_svc.h
@@ -74,6 +74,9 @@
 			 void *handle,
 			 uint64_t flags);
 
+/* Helper to enter a Secure Partition */
+uint64_t spm_sp_call(uint32_t smc_fid, uint64_t x1, uint64_t x2, uint64_t x3);
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __SPM_SVC_H__ */