upl: Add support for reading a upl handoff

Universal Payload provides a standard way of handing off control between
two firmware phases. Add support for reading the handoff information into
a structure.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index dc5fcdb..484f9e1 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -16,6 +16,7 @@
 CONFIG_FIT_CIPHER=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_BOOTMETH_ANDROID=y
+CONFIG_UPL=y
 CONFIG_LEGACY_IMAGE_FORMAT=y
 CONFIG_MEASURED_BOOT=y
 CONFIG_BOOTSTAGE=y