cactus: re-align secure partition id

According to [1] and [2] secure partition ids are defined from
0x8001 to 0xfffe. Update the cactus test payload and TFTF such
that it uses the appropriate IDs.
0x8000 and 0xffff are reserved FF-A IDs respectively for the SPMC
and the SPMD.
Conversely in the NWd, the Hypervisor ID is 0 and VMs are numbered
in the range of 1 to 0x7fff.

[1] https://trustedfirmware-a.readthedocs.io/en/latest/components/
secure-partition-manager.html#ffa-id-get
[2] https://review.trustedfirmware.org/c/hafnium/hafnium/+/5165

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I3e9786212b227e6637a7650e60ddc4e59ad05a46
diff --git a/spm/common/sp_helpers.h b/spm/common/sp_helpers.h
index 7096daf..965f799 100644
--- a/spm/common/sp_helpers.h
+++ b/spm/common/sp_helpers.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, Arm Limited. All rights reserved.
+ * Copyright (c) 2018-2020, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -11,9 +11,7 @@
 #include <tftf_lib.h>
 #include <ffa_helpers.h>
 
-#define SPM_VM_ID_FIRST                 (1)
-#define SPM_VM_ID_SECOND                (2)
-#define SPM_VM_ID_THIRD                 (3)
+#define SPM_VM_ID_FIRST                 SP_ID(1)
 
 #define SPM_VM_GET_COUNT                (0xFF01)
 #define SPM_VCPU_GET_COUNT              (0xFF02)