mt76: usb: fix static tracepoints

Add submit_urb and rx_urb static tracepoints in mt76-usb module.
Move trace_mac_txstat_fetch in mt76x02_mac_load_tx_status routine
in order to be available to usb drivers. Moreover remove
no longer used mt76x0/trace.{c,h}

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>