Allow multiple profiles to be added as part of boot.prof

Extend PRODUCT_DEX_PREOPT_BOOT_IMAGE_PROFILE_LOCATION such that
multiple text-based profiles can be fed to profman to be included
in boot.prof

BUG: 70292748
Test: profman with --dump-only option shows that additional
      text-based profiles are also being read if they have
      been added to PRODUCT_DEX_PREOPT_BOOT_IMAGE_PROFILE_LOCATION

Change-Id: I8a6437a323e43b61612c67038abdde200607c513