drivers: udc_nrf: Do not use nrf usbd common

This is preparatory commit for former nrfx USBD refactor. The refactor
towards native driver will only be performed on the udc driver (old USB
stack driver will continue to use nrf usbd common until it is removed).

Code is copied from nrf_usbd_common.c with minimal changes:
  * nrf_usbd_common_irq_handler renamed to nrf_usbd_irq_handler
  * usbd_enable renamed to nrf_usbd_peripheral_enable
  * all non-static nrf_usbd_common functions have prefix changed to
    nrf_usbd_legacy and are changed to static
  * functions not used by udc nrf driver are removed
  * braces are moved inside #if to pass compliance checks

No functional changes.

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