media: cros-ec-cec: Manage an array of ports

To support multiple CEC ports, change cros_ec_cec to contain an array of
ports, each with their own CEC adapter, etc.

For now, only create a single port and use that port everywhere, so
there is no functional change. Support for multiple ports will be added
in the following patches.

Signed-off-by: Reka Norman <rekanorman@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>