check_elf_file: check prebuilts are aligned

WARNING: two things still need to be done
1. this should probably only be enabled when PAGE_SIZE
   is undefined, but I'm curious what other targets
   break now.
2. we may need a per-prebuilt way to disable this,
   like some of the other settings here.

For prebuilts added onto a device, we can check the
page alignment matches the one declared in the build
configuration.

Bug: 342466032
Test: manually, by changing the script to require 64 KB
  alignment, I was able to see its errors on new targets.
Change-Id: Ic118245e64d67204bf5fa740a3e1afb7325b34f5