sourcedr: Find system files from vendor sources

This commit adds list_system_file_from_vendor_source.py, which will list
all system files that are from vendor/* or device/*.

Test: ./list_system_file_from_vendor_source.py \
  --ninja-deps out/.ninja_deps \
  out/combined-$target.ninja

Change-Id: Icbb36590ce4e99199785c64df2668452fd861e15