doc:it_IT: align translation to mainline

The patch translates the following patches in Italian:

1fb12b35 kbuild: Raise the minimum required binutils version to 2.21
9c3c0c20

 isdn: remove isdn4linux

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>