uboot-imx

buildman: Automatically create a config file if needed

If there is no ~/.buildman file, buildman currently complains and exists. To
make things a little more friendly, create an empty one automatically. This
will not allow things to be built, but --fetch-arch can be used to handle
that.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>