SPMD: generate and add Secure Partition blobs into FIP

Till now TF-A allows limited number of external images to be made part
of FIP. With SPM coming along, there may exist multiple SP packages
which need to be inserted into FIP. To achieve this we need a more
scalable approach to feed SP packages to FIP.

This patch introduces changes in build system to generate and add SP
packages into FIP based on information provided by platform.
Platform provides information in form of JSON which contains layout
description of available Secure Partitions.
JSON parser script is invoked by build system early on and generates
a makefile which updates FIP, SPTOOL and FDT arguments which will be
used by build system later on for final packaging.

"SP_LAYOUT_FILE" passed as a build argument and can be outside of TF-A
tree. This option will be used only when SPD=spmd.

For each SP, generated makefile will have following entries
     - FDT_SOURCES	+=	sp1.dts
     - SPTOOL_ARGS	+= 	-i sp1.img:sp1.dtb -o sp1.pkg
     - FIP_ARGS		+=	--blob uuid=XXXX-XXX...,file=SP1.pkg

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: Ib6a9c064400caa3cd825d9886008a3af67741af7

docs/getting_started/build-options.rst

@@ -522,6 +522,11 @@ Common build options
 -  ``SPM_MM`` : Boolean option to enable the Management Mode (MM)-based Secure
    Partition Manager (SPM) implementation. The default value is ``0``.
 
+-  ``SP_LAYOUT_FILE``: Platform provided path to JSON file containing the
+   description of secure partitions. Build system will parse this file and
+   package all secure partition blobs in FIP. This file not necessarily be
+   part of TF-A tree. Only avaialbe when ``SPD=spmd``.
+
 -  ``SP_MIN_WITH_SECURE_FIQ``: Boolean flag to indicate the SP_MIN handles
    secure interrupts (caught through the FIQ line). Platforms can enable
    this directive if they need to handle such interruption. When enabled,