sandbox: log: Avoid build error with !CONFIG_LOG

The pr_cont_test.c test requires CONFIG_LOG since it directly accesses
fields in global_data that require it. Move the test into the CONFIG_LOG
condition to avoid build errors.

Enable CONFIG_LOG on sandbox (not sandbox_spl, etc.) so that we still run
this test. This requires resyncing of the configs.

Signed-off-by: Simon Glass <sjg@chromium.org>