Romlib makefile refactoring and script rewriting ...

The features of the previously existing gentbl, genvar and genwrappers
scripts were reimplemented in the romlib_generator.py Python script.
This resulted in more readable and maintainable code and the script
introduces additional features that help dependency handling in
makefiles. The assembly templates were separated from the script logic
and were collected in the 'templates' directory.

The targets and their dependencies were reorganized in the makefile and
the dependency handling of included index files is possible now.
Incremental build is available in case of modifying the index files.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: I79f65fab9dc5c70d1f6fc8f57b2a3009bf842dc5