Cleanup: move VINTF fragments into VAPEX

VINTF fragments for Power VAPEX were installed in /vendor/etc as a
workaround when VINTF fragments in VAPEX were not supported.

Bug: n/a
Test: m && launch_cvd
      # power/power-stat services are running
Change-Id: I0243a0bd2f2dd597260f73a3994cf81db213daf7