This fixes the following error for CRIU on AArch64 kernels with
CONFIG_ARM64_64K_PAGES=y.

  Error (cr-restore.c:2828): Can't mmap section for restore code

This occurred because the address being requested (0x16000 in
one case) was not page aligned.

Also change the capitalization of the pie_size() macro to make it
clear that the value is not necessarily a build-time constant.
Signed-off-by: Christopher Covington <cov@codeaurora.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>