extract_utils: allow filename only symlink

With this change both of these examples will generate the same
blueprint:
vendor/etc/hal_uuid_map_config.xml;SYMLINK=hal_uuid_map_c000850.xml
vendor/etc/hal_uuid_map_config.xml;SYMLINK=vendor/etc/hal_uuid_map_c000850.xml

Change-Id: I11da9dfec885ade5c7e7a66406c496973ff82486

Author: luk1337

extract_utils/makefiles.py

@@ -601,6 +601,8 @@ def write_symlink_package(
     encoder: JSONEncoder,
 ):
     symlink_target = f'/{file.dst}'
+    if '/' not in symlink:
+        symlink = f'{os.path.dirname(file.dst)}/{symlink}'
     part, location = symlink.split('/', 1)
     package_name = symlink.replace('/', '_').replace('.', '_')