vbe: Support reading the next SPL phase via VBE

Add an SPL loader to obtain the next-phase binary from a FIT provided
by the VBE driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/Makefile b/boot/Makefile
index 19d628d..e5c2790 100644
--- a/boot/Makefile
+++ b/boot/Makefile
@@ -49,3 +49,4 @@
 
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE) += vbe.o vbe_request.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE_SIMPLE) += vbe_simple.o
+obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE_SIMPLE_FW) += vbe_simple_fw.o