rtw88: show current regulatory in tx power table

In the transmit power table, it is important to know what the regulatory
currently is. For different regulatories, there are different
transmit power limits. Show which regulatory the driver is currently
using.

Signed-off-by: Tzu-En Huang <tehuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200925061219.23754-6-tehuang@realtek.com