Introduce .editorconfig

Introduce .editorconfig

A few weeks ago, Jose Fonseca suggested [0] we use .editorconfig files
to try and enforce the formatting of the code, to which Michel Dänzer
suggested [1] we start by importing the existing .dir-locals.el
settings. The first draft was discussed in the RFC [2].

These .editorconfig are a first step, one that has the advantage of
requiring little to no intervention from the devs once the settings
files are in place, but the settings are very limited. This does have
the advantage of applying while the code is being written.
This doesn't replace the need for more comprehensive formatting tools
such as clang-format & clang-tidy, but those reformat the code after
the fact.

[0] https://lists.freedesktop.org/archives/mesa-dev/2016-June/121545.html
[1] https://lists.freedesktop.org/archives/mesa-dev/2016-June/121639.html
[2] https://lists.freedesktop.org/archives/mesa-dev/2016-July/123431.html

Acked-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Acked-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>