usb: gadget: aspeed: Rework the reset logic

We had some dodgy code using the speed setting to decide whether a
port reset would reset the device or just enable it.

Instead, if the device is disabled and has a gadget attached, a
reset will enable it. If it's already enabled, a reset will
reset it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>