mt76: mt7615: enable beacon filtering by default for offload fw

In order to reduce cpu cycles, enable hw beacon filter by default if
the device is running offload fw with sta only interfaces.
Disable runtime pm for multi-vif scenario.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>