Notice files for prebuilt_etc are included in APEX

This change fixes a bug that notice files for some module type (e.g.
prebuilt_etc) were not included in APEX. This happened because we relied
on WalkPayloadDeps which actually doesn't traverse module types that
don't implement ApexModule interface. prebuilt_etc is one such module
type. Fixing the problem by also iterating the filesInfo array which
has info about all modules that are included in the APEX.

Bug: 166575301
Test: m com.android.tzdata and inspect the built artifact.
NOTICE.html.gz is there.

Change-Id: Iceb055b60184aef2a3e65e44680304853eb79a53