Tools: Support out-of-tree secure partition build

Support TF-M to build mulitple scure partition whose source code folder
is maintained outside TF-M repo.

 - Rename TFM_EXTRA_MANIFEST_LIST_PATH to TFM_EXTRA_MANIFEST_LIST_FILES
   to indicate the out-of-tree secure partition manifest list files.
 - Add config TFM_EXTRA_PARTITION_PATHS to indicate the out-of-tree
   secure partition directories
 - Add attribute output_path in manifest list to enable out-of-tree
   partition to specify the directory of its generated files.
 - Support relative manifest path in the manifest list of an out-of-tree
   secure partition.
   For example, a manifest path can be set as a relative path to the
   manifest list file. Therefore, the manifest path can be independent
   to out-of-tree secure partitionsourece code path.

Change-Id: I743b458c405d2a9af43d4f234e52f80cdb545103
Signed-off-by: David Hu <david.hu@arm.com>
4 files changed