x86: apl: Re-enable loading of SPL

At present the SPL loader is not included in the TPL image so SPL cannot
be loaded. Fix it by including this file for both SPL and TPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: c87f9ce2 ("x86: Don't build some unused objects in TPL")
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>