binman: build_from_git: Add optional make path inside git repo

Add optional argument make_path to build_from git. The new argument
allows specifying the path to a Makefile in case it is not in the root
of the git repo.
Also adjust the corresponding test.

Signed-off-by: Leonard Anderweit <l.anderweit@phytec.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed