doc:it_IT: add translation for I2C summary and protocol

This patch adds the italian translation for I2C subsystem summary and
protocol. Plus, a reference in the subsystem-apis page.

Signed-off-by: Davide Benini <davide.benini@gmail.com>
Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240209220126.28042-1-federico.vaga@vaga.pv.it