usb: usb251xb: support usage case without I2C control

Currently, the usb251xb assumes i2c control. But from HW point of
view, the hub supports usage case without any i2c, we only want the
gpio controls.

Refactor the code so that register writes for configuration are only
performed if the device has a i2c_client provided and also register as
a platform driver. This allows the driver to be used to manage GPIO
based control of the device.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20250825234509.1041-4-jszhang@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>