Enable execute-only memory layouts by default.

This enables execute-only memory (XOM) layouts to be used by default in
the build system. As of now, there's only support for ARM64 devices, so
this only affects those. Since userland XOM requires kernel support,
devices without the necessary support will continue to allow pages
marked execute-only to be read and they should be unaffected by this.

Bug: 77958880
Test: Device with and without kernel support boot.
Test: Binary throws segfault when reading from XOM on supported device.
Test: Debugger works and stack traces are still generated correctly.
Test: Teamfooding, stable during regular usage.

Change-Id: I8db4235c8e60eea6d701bdf3c43b79a06d6b01cd