uboot-imx

buildman: Allow specifying a range of commits to build

Adjust the -b flag to permit a range expression as well as a branch.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Tested-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>