rtw88: support SAR via kernel common API

Register cfg80211_sar_capa with type NL80211_SAR_TYPE_POWER and four
frequency ranges for configurations in unit of 0.25 dBm. And handle
callback set_sar_specs.

Originally, TX power has three main parameters, i.e. power base,
power by rate, and power limit. The formula can be simply considered
as TX power = power base + min(power by rate, power limit). With the
support of SAR which can be treated as another power limit, there is
one more parameter for TX power. And the formula will evolve into
TX power = power base + min(power by rate, power limit, power sar).

Besides, debugfs tx_pwr_tbl is also refined to show SAR information.
The following is an example for the difference.
Before supporting SAR,
-----------------------------------
...
path rate pwr base (byr lmt ) rem
A CCK_1M 66(0x42) 78 -12 ( 12 -12) 0
A CCK_2M 66(0x42) 78 -12 ( 8 -12) 0
...
-----------------------------------
After supporting SAR and making some configurations,
-----------------------------------
...
path rate pwr base (byr lmt sar ) rem
A CCK_1M 62(0x3e) 78 -16 ( 12 -12 -16) 0
A CCK_2M 62(0x3e) 78 -16 ( 8 -12 -16) 0
...
-----------------------------------

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211220093656.65312-1-pkshih@realtek.com