test(ivy): S-EL0 partition using VHE

Starting from [1], Cactus remains the sample S-EL1 partition.
Ivy remains the sample "S-EL0 partition" either using the shim at S-EL1
(as of today), or leveraging Hafnium VHE (reason for this change).
The same code base is re-used by adding the IVY_SHIM toggle. IVY_SHIM=1
is default using the shim, or 0 to use VHE (and strip the shim out).
Using svc helper from spm/common/aarch64/sp_arch_helpers.S

We must modify generate_json.sh so it only adds the partition
information to the layout file for the sp given in arg1. This allows
the ability for sp's to pass flags to the script such as IVY_SHIM which
is used to vary the dts file included for ivy.

Typical build command for a VHE-enabled Ivy partition:
make CROSS_COMPILE=aarch64-none-elf- PLAT=fvp DEBUG=1 TESTS=spm
    ARM_ARCH_MINOR=5 BRANCH_PROTECTION=1 IVY_SHIM=0 ivy -j8

The intent is to create a dedicated tftf_config build config for the
VHE-enabled build in the CI.

[1] https://trustedfirmware-a-tests.readthedocs.io/en/latest/getting_started/build.html#cactus-and-ivy

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
Change-Id: I34125b375b043c61c44ede558802d8ae757bd51f
diff --git a/tools/generate_dtb/generate_dtb.sh b/tools/generate_dtb/generate_dtb.sh
index 564c2a0..f4a4271 100755
--- a/tools/generate_dtb/generate_dtb.sh
+++ b/tools/generate_dtb/generate_dtb.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 
 #
-# Copyright (c) 2018-2020, Arm Limited. All rights reserved.
+# Copyright (c) 2018-2022, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -12,13 +12,14 @@
 # $1 = image_name (lowercase)
 # $2 = path/to/file.dts
 # $3 = build/$PLAT/$BUILD_TYPE/
+# $4 = path to store the dtb generated by this script
 
 ORIGINAL_DTS=$2
 MAPFILE="$3/$1/$1.map"
 EXTRA_DTS="$3/$1/$1_extra.dts"
 COMBINED_DTS="$3/$1/$1_combined.dts"
 PREPROCESSED_DTS="$3/$1/$1_preprocessed.dts"
-GENERATED_DTB="$3/$1.dtb"
+GENERATED_DTB=$4
 
 # Look for the start and end of the sections that are only known in the elf file
 # after compiling the partition.