mt76: add 6 GHz band support in mt76_sar_freq_ranges

Add new frequencies support in mt76_sar_freq_ranges[]
* 5945 - 6165
* 6165 - 6405
* 6405 - 6525
* 6525 - 6705
* 6705 - 6865
* 6865 - 7125

Reviewed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>