drivers: nrf_wifi: Fix deadlock in display scan and recovery

When running Zperf traffic + scan in the background eventual we hit a
deadlock:

 * sysworkq: recovery->stop_zep->vif_lock->hal_disable->wait lock_rx
 * nrf70_bh_wq: event_tasklet->lock_rx->disp_scan_done->
             disp_scan_res_get_zep-> waiting on vif_lock

The traffic triggers recovery (another bug) and conflicts with display
scan.

Fix by moving scan results processing to system workqueue instead of
doing it in the FMAC event callback context, this is how supplicant scan
also works.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>