Use abspath to dereference $BUILD_BASE ...

If the user tries to change BUILD_BASE to put the build products outside
the build tree the compile will fail due to hard coded assumptions that
$BUILD_BASE is a relative path. Fix by using $(abspath $(BUILD_BASE))
to rationalize to an absolute path every time and remove the relative
path assumptions.

This patch also adds documentation that BUILD_BASE can be specified by
the user.

Signed-off-by: Grant Likely <grant.likely@arm.com>
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: Ib1af874de658484aaffc672f30029b852d2489c8

sptool: append cert_tool arguments. ...

To support secure boot of SP's update cert tool arguments while
generating sp_gen.mk which in turn is consumed by build system.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I2293cee9b7c684c27d387aba18e0294c701fb1cc

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