nrf_usbd_common: Refactor interrupt handling code

Ensure strict order within interrupt processing to eliminate workaround
in IN transfer acknowledged handler. EPDATASTATUS and DMA done events
are processed in a way that eliminates the possibility for race condions
between interrupt handler and host IN tokens.

Store last started DMA endpoint and use it in common handler for all DMA
finished events. Unify use of ep dma waiting variable because atomics
only make sense if all accesses are through atomic functions - here the
accesses are guarded with critical section.

Do not disable SETUP interrupt when DMA transfers data on endpoint 0 but
simply postpone handling if currently active DMA is on endpoint 0.

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