soong: Add product variable DevicePageSizeAgnostic

The product variable DevicePageSizeAgnostic will determine
whether AOSP is kernel page size agnostic or not.

Test: source build/envsetup.sh
      lunch aosp_cf_arm64_phone_pgagnostic
      m
      cat out/soong/build.aosp_cf_arm64_phone_pgagnostic.ninja | grep __BIONIC_NO_PAGE_SIZE_MACRO
Bug: 289419664
Change-Id: I33a1a4f1967d7e78432b7b8d90357d16b2002dcc