mac80211: add support for driver tx power reporting

The configured tx power is often limited by hardware capabilities,
channel settings, antenna configuration, etc.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
[fix tracing compilation]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc include/net/mac80211.h
Simple merge

diff --cc net/mac80211/cfg.c
Simple merge

diff --cc net/mac80211/driver-ops.h
Simple merge

diff --cc net/mac80211/trace.h
Simple merge