vbe: Support selecting operations by SPL phase

VBE supports booting firmware during the SPL phases, i.e. so that VPL can
start SPL and SPL can start U-Boot.

It also supports booting an OS, when in U-Boot.

As a first step towards these features, add functions to indicate the
current VBE phase. The firmware selection is done in VPL and the OS
selection is done in U-Boot proper.

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