rtw89: add UK to regulation type

Add RTW89_UK to enum rtw89_regulation_type.
The follow-up commit will configure the corresponding values for it
to TX power tables.

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/20220318023214.32411-2-pkshih@realtek.com