Move TSP private declarations into separate header

Move the TSP private declarations out of tsp.h and into a new
header, tsp_private.h. This clarifies the TSP interface to the TSPD.

Change-Id: I39af346eeba3350cadcac56c02d97a5cb978c28b
diff --git a/bl32/tsp/aarch64/tsp_entrypoint.S b/bl32/tsp/aarch64/tsp_entrypoint.S
index 75ee443..555f120 100644
--- a/bl32/tsp/aarch64/tsp_entrypoint.S
+++ b/bl32/tsp/aarch64/tsp_entrypoint.S
@@ -32,6 +32,7 @@
 #include <asm_macros.S>
 #include <tsp.h>
 #include <xlat_tables.h>
+#include "../tsp_private.h"
 
 
 	.globl	tsp_entrypoint