usb: dwc2: gadget: Disable enabled HW endpoint in dwc2_hsotg_ep_disable

Check if endpoint is enabled during dwc2_hsotg_ep_disable() function
processing and call dwc2_hsotg_ep_stop_xfr() to disable it and flush
associated FIFO.

Move dwc2_hsotg_ep_stop_xfr() and dwc2_hsotg_wait_bit_set() functions
upper before dwc2_hsotg_ep_enable and dwc2_hsotg_ep_disable function
definitions.

Signed-off-by: Vahram Aharonyan <vahrama@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>