mt76: rename mt76x02_util.h in mt76x02.h

Rename mt76x02_util.h header file in mt76x02.h since now contains
all mt76x02 related definitions and not just utility routines
declarations

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