linker_config_src in filesystem may read filegroup

Add "path" annotation to the linker_config_src property in filesystem
module to read a filegroup as a source.

Bug: 365670526
Test: lunch aosp_cf_x86_64_phone_soong_system-trunk_staging-userdebug
      && m
Change-Id: I96abb376640eea009f03841866b8c7b5d95917fa