Enable merge_json.py to handle multiple input files

Rewrite merge_json.py to enable merging multiple input files into a
single JSON file. Also adding a mechanism for update the relative paths
in the JSON file, so their base directory will be the parent directory
of the merged JSON file.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: Ia9452d1e1a0a7916c48e61ff4cbe0986fa370730
1 file changed