x86: Support booting with TPL

Some boards want to use TPL as the first phase of U-Boot. This allows
selection of A or B SPL phases, thus allowing the memory init to be
upgraded in the field.

Add a new Kconfig option for this.

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