[U-Boot] [PATCH] genconfig.py: Print defconfig next to warnings

[sjg at google.com]

At present we sometimes see warnings of the form:

/tmp/tmpMA89kB:36: warning: overriding the value of CMD_SPL.
	Old value: "y", new value: "y".

This is not very useful as it does not show whch defconfig file it relates
to. Update the tool to show this.

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

 tools/buildman/kconfiglib.py | 22 ++++++++++++++++------
 tools/genboardscfg.py        |  7 +++++--
 2 files changed, 21 insertions(+), 8 deletions(-)

Applied to u-boot-dm, thanks!