dt-bindings: usb: mtu3: remove support VBUS detection of extcon

dt-bindings: usb: mtu3: remove support VBUS detection of extcon

Due to no platforms use a multi-funtion pin to detect VBUS
status until now when support dual role mode, prefer not to
support it anymore;
Another reason is that the controller doesn't support idle status,
the dual role port works as device or as host, using an IDDIG pin
is good enough, this will help to save another multi-function pin;
And fix a typo of 'neede';
Last modify example using VBUS to turn on/off device, for device
only mode, the driver doesn't get extcon.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1626340078-29111-2-git-send-email-chunfeng.yun@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>