include: move qemu_*_exec_dir() to cutils

The function is required by get_relocated_path() (already in cutils),
and used by qemu-ga and may be generally useful.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220525144140.591926-2-marcandre.lureau@redhat.com>