[coreboot] make gitconfig not working for me with git 1.9.1

[Nico Huber]

On 24.02.2018 01:10, mturney at codeaurora.org wrote:
> 
> Errors I receive on command-line strongly point to this commit:
> 
> commit fda071ca7a17614a58c0812c28b14a417471b915
> Author: Alex Thiessen <alex.thiessen.de+coreboot at gmail.com>
> Date:   Sat Jan 13 17:05:31 2018 +0000
> 
>     util/gitconfig: Make gitconfig.sh support gitfile

Yes, this is obviously the culprit. The --git-path switch to
git-rev-parse wasn't always available.

Alex, Stefan, can you please fix the issue (I already tried to revert,
but it was part of a longer train, so not that easy). Generally, before
using `git rev-parse --git-path` you have to test if it is supported.
In flashrom, I added a check if it just returns `--git-path` (4164c541).

Nico