usb: dwc3: gadget: don't rely on jiffies while holding spinlock

__dwc3_gadget_wakeup() is called while holding a spinlock, then depends on
jiffies in order to timeout while polling the USB core for a link state
update. In the case the wakeup failed, the timeout will never happen and
will also cause the cpu to stall until rcu_preempt kicks in.

This switches to a "decrement variable and wait" timeout scheme.

Signed-off-by: Nicolas Saenz Julienne <nicolassaenzj@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>