sandbox: Allow to execute from RAM

sandbox: Allow to execute from RAM

With efi_loader, we may want to execute payloads from RAM. By default,
permissions on the RAM region don't allow us to execute from there though.

So let's change the default allocation scheme for RAM to also allow
execution from it. That way payloads that live in U-Boot RAM can be
directly executed.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Alexander Graf <agraf@suse.de>