extcon: usbc-tusb320: Make typec-power-opmode optional

The driver returned an error in the probe function when a usb c
connector is configured in the DT without a "typec-power-opmode"
property. This property is used to initialize the CURRENT_MODE_ADVERTISE
register of the TUSB320, which is unused when operating as a UFP.
Requiring this property causes unnecessary configuration overhead and
inconsistency with the USB connector DT bindings, which do not specify
it as required.

This change makes typec-power-opmode optional. When the property is not
present, the driver will skip programming the CURRENT_MODE_ADVERTISE
register and rely on the hardware default.

Signed-off-by: Yannis Bolliger <yannis.bolliger@protonmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Link: https://lore.kernel.org/lkml/aPKZJ6WTZlhSOyST@yaene-desktop/