usb: cdns3-starfive: Add extcon usb gadget state with always connected

usb: cdns3-starfive: Add extcon usb gadget state with always connected

Add extcon usb gadget state and set usb gadget state as connected.

The cdns3-starfive usb c port in visionfive2 board only has usb
d-/d+ lines and vbus and ground lines are used for power supply.
Because of the H/W limitation, it is not possible to detect usb
c port connected state.

In Tizen, deviced configures usb gadget functions only with the
usb connected state, so, to support usb gadget functionality,
the usb state should be set.

Change-Id: I3e3a25a726c7205b3d9a5fd96d8557562bfda81f
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>