GitLab

As the file extension *.inc is quite ambiguous, Github's linguist [1]
tends to classify such files not as Bitbake include files, but something
entirely different.

This commit overrides the default behavior of linguist to classify these
files correctly.

[1] https://github.com/github/linguist

Signed-off-by: Dennis Menschel <menschel-d@posteo.de>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>