Rename local usbd copy from nrfx_usbd to nrf_usbd_common and use it in
both USB stacks. Renaming header to nrf_usbd_common.h allows breaking
changes in exposed interface. Mark all doxygen comments as internal
because local usbd copy should not be treated as public interface
because we are under refactoring process that aims to arrive at native
driver and therefore drop nrf_usbd_common in the future.
Use Zephyr constructs directly instead of nrfx glue macros.
No functional changes.
Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>
