doc:it_IT: align translation to mainline

The patch translates the following patches in Italian:

d9d7c0c4 docs: Note that :c:func: should no longer be used
83e8b971 sphinx.rst: Add note about code snippets embedded in the text
cca5e0b8 Documentation: PGP: update for newer HW devices

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