drivers: udc_dwc2: Properly revive STALLed endpoints

DWC2 documentation unfortunately assigns somewhat confusing semantics to
endpoint "enable"/"disable" and "activate"/"deactivate". The Zephyr USB
device stack endpoint enable/disable refers to DWC2 activate/deactivate.
The DWC2 endpoint enable/disable actions can be loosely referred to
Zephyr USB stack enqueue/dequeue.

Rename the functions and rework internal working to match DWC2
Programming Guide. This makes endpoint halt work as expected by the
stack and therefore fixes all classes that rely on correct STALL
handling. Most notable STALL user is the Mass Storage class.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>