dt-bindings: net: wireless: mt76: add clock description for MT7986.

Add clocks and clock-names for MT7986.

Reviewed-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>