dt-bindings: vendor-prefixes: document Octavo Systems oct prefix

Octavo Systems is an American company specializing in design and
manufacturing of System-in-Package devices.

The prefix is already in use for the Octavo Systems OSD3358-SM-RED
device tree, but was so far undocumented. Fix this.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Neeraj Dantu <neeraj.dantu@octavosystems.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>