wifi: rtw89: regd: refactor init/setup flow and prototype

The regulatory and wiphy setup should be done in rtw89_regd_setup(). And,
what rtw89_regd_init() should do is to initialize target regulatory domain
(regd), if and only if one is programmed in efuse. Since HW is registered
after rtw89_regd_setup() and before rtw89_regd_init(), do not fill fields
of regulatory in rtw89_regd_init(). So, move the regulatory->reg_6ghz_power
assignment into rtw89_regd_setup().

Besides, rtw89_regd_notifier is assigned in rtw89_regd_setup() instead of
rtw89_regd_init(). To reduce confusion, stop passing rtw89_regd_notifier to
rtw89_regd_init(). And, rename rtw89_regd_init() to rtw89_regd_init_hint().

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250120032723.19042-4-pkshih@realtek.com