16k: Get the page size dynamically

Android V will support page size agnostic targets. For
frameworks, getpagesize() will be used instead of the
hardcoded value for page size.

Bug: 298041921
Test: source build/envsetup.sh
      lunch aosp_cf_arm64_phone_pgagnostic
      m
Change-Id: I62c94da767a79df9515d5b9cbb93764508a0f023