mt76: mt7915: register per-phy HE capabilities for each interface

The capabilities for the HE interfaces are generated from the capabilities
reported by the firmware.

This should move to common file once we got other HE devices support.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>