[][mac80211][wifi6][mt76][Fix txpower sku issues]

[Description]
Fix txpower sku issues
1. Refactor mt76 update txpower flow, we only consider CCK and OFDM power value as maximum.
   And also consider whether the sku is enable.
2. Refactor txpower control flow. If we don't fill path table in dts, mt76 will disable backoff sku.

[Release-log]
N/A

Change-Id: I3a8a9f66ff298565cb3280c83eccede1a2267ba8
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8143625
2 files changed