support: add autobuild toolchain config fragments

We currently have a list of toolchain configurations that are used by
the autobuilders at [1]. However, this makes it a little more difficult
for people to use these configurations, and also to have a different
list of configurations for different branches. For example if a new
architecture is introduced, the 2017.02.x branch doesn't have support
for this architecture yet so it shouldn't try to run those configs.

Therefore, include the autobuild config fragments directly in Buildroot,
so they can be branched together with the rest. We create a new
directory under support/ to store them.

Generated with
wget -nd --no-parent --recursive http://autobuild.buildroot.net/toolchains/configs/

The index.html file is removed.

The toolchain-configs.csv file is adapted so the URLs become relative
paths pointing to the config fragments.

[1] http://autobuild.buildroot.net/toolchains/configs/toolchain-configs.csv



Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>