wifi: rtw89: regd: indicate if regd_UK TX power settings follow regd_ETSI

Before adopting regd_UK TX power settings, some certifications are needed
and might be platform-level. Without that, should adopt regd_ETSI TX power
settings. But for now, there is no way to inform driver of it yet. So, add
a flag first. But for now, comprehensively use regd_ETSI TX power settings
to restrict regd_UK.

Plan to define an ACPI DSM function to inform driver whether to use regd_UK
own TX power settings or not afterwards.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250416081241.36138-4-pkshih@realtek.com