[U-Boot] [PATCH 15/53] binman: Show a helpful error when a DT property is missing

[sjg at google.com]

At present a Python exception is raised which does not show the node
information. Add a more helpful exception in this case.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 tools/dtoc/fdt.py      | 23 ++++++++++++++++++++---
 tools/dtoc/test_fdt.py | 21 +++++++++++++++++++++
 2 files changed, 41 insertions(+), 3 deletions(-)

Applied to u-boot-dm, thanks!