wifi: mt76: fix backoff fields and max_power calculation

wifi: mt76: fix backoff fields and max_power calculation

The maximum power value may exist in either the data or backoff field.
Previously, backoff power limits were not considered in txpower reporting.
This patch ensures mt76 also considers backoff values in the SKU table.

Also, each RU entry (RU26, RU52, RU106, BW20, ...) in the DTS corresponds
to 10 stream combinations (1T1ss, 2T1ss, 3T1ss, 4T1ss, 2T2ss, 3T2ss,
4T2ss, 3T3ss, 4T3ss, 4T4ss).

For beamforming tables:
- In connac2, beamforming entries for BW20~BW160, and OFDM do not include
  1T1ss.
- In connac3, beamforming entries for BW20~BW160, and RU include 1T1ss,
  but OFDM beamforming does not include 1T1ss.

Non-beamforming and RU entries for both connac2 and connac3 include 1T1ss.

Fixes: b05ab4be9fd7 ("wifi: mt76: mt7915: add bf backoff limit table support")
Signed-off-by: Allen Ye <allen.ye@mediatek.com>
Co-developed-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Link: https://patch.msgid.link/8fa8ec500b3d4de7b1966c6887f1dfbe5c46a54c.1771205424.git.ryder.lee@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>