wifi: rtw89: regd/acpi: update field definition to specific country in UNII-4 conf

Originally, fields of ACPI DSM function 6 were handled for countries
following specific regulatory.
	BIT(0) for countries following FCC regulatory
	BIT(1) for countries following IC regulatory

Now, update to the following (one field for one specific country).
	BIT(0) for country US
	BIT(1) for country CA

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250709065006.32028-3-pkshih@realtek.com