16k: soong: Add flag Device_page_size_agnostic

The flag Device_page_size_agnostic will determine whether
AOSP is kernel page size agnostic or not.

Test: source build/envsetup.sh
      lunch aosp_raven_64-userdebug
      m -j$(nproc)
      cat out/soong/build.aosp_raven_64.ninja | grep TARGET_PAGE_SIZE_AGNOSTIC
Bug: 289419664
Change-Id: I0604db64a3b44db63f93773be003cdd44e0a867b