x86: fsp: Add more debugging for silicon init

If locating the FSP header hangs for whatever reason it is useful to see
where it got stuck. Add a debug print. Also show the address of the FSP-S
entry point as a sanity check.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>