FWU: Add Generic BL2U FWU image support in BL2 ...

The Firmware Update (FWU) feature needs support for an optional
secure world image, BL2U, to allow additional secure world
initialization required by FWU, for example DDR initialization.

This patch adds generic framework support to create BL2U.

NOTE: A platform makefile must supply additional `BL2U_SOURCES`
      to build the bl2u target. A subsequent patch adds bl2u
      support for ARM platforms.

Change-Id: If2ce036199bb40b39b7f91a9332106bcd4e25413

Add uppercase macro to build_macros.mk ...

This patch adds `uppercase` macro to prepare IMAGE_BLxx defines
used for conditional compilation and to prepare variables used
for defining BL source and linker file names.

This change is needed for upcoming BL images that can have names
which uses both letters and numbers.

Change-Id: I05ce9bcd0d221a54db92c0fe3ad28e9e0080ed2e

Make: fix dependency files generation ...

Currently, if no make goal is specified in the command line, 'all'
is assumed by default, but the dependency files are not generated.
This might lead to a successful but inconsistent build. This patch
provides a fix to the problem.

Change-Id: I0148719e114dbdbe46f8a57c7d05da7cbc212c92

Rework Makefile ...

This patch is a complete rework of the main Makefile. Functionality
remains the same but the code has been reorganized in sections in
order to improve readability and facilitate adding future extensions.

A new file 'build_macros.mk' has been created and will contain common
definitions (variables, macros, etc) that may be used from the main
Makefile and other platform specific makefiles.

A new macro 'FIP_ADD_IMG' has been introduced and it will allow the
platform to specify binary images and the necessary checks for a
successful build. Platforms that require a BL30 image no longer need
to specify the NEED_BL30 option. The main Makefile is now completely
unaware of additional images not built as part of Trusted Firmware,
like BL30. It is the platform responsibility to specify images using
the macro 'FIP_ADD_IMG'. Juno uses this macro to include the BL30
image in the build.

BL33 image is specified in the main Makefile to preserve backward
compatibility with the NEED_BL33 option. Otherwise, platform ports
that rely on the definition of NEED_BL33 might break.

All Trusted Board Boot related definitions have been moved to a
separate file 'tbbr_tools.mk'. The main Makefile will include this
file unless the platform indicates otherwise by setting the variable
'INCLUDE_TBBR_MK := 0' in the corresponding platform.mk file. This
will keep backward compatibility but ideally each platform should
include the corresponding TBB .mk file in platform.mk.

Change-Id: I35e7bc9930d38132412e950e20aa2a01e2b26801