wifi: rtw89: acpi: introduce method evaluation function for reuse

The following implementations will evaluate different ACPI methods, but
the pre-process flow of them are the same. So, introduce a function for
these pre-process things. Besides, also change ACPI RTAG method to call
this function.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250326020643.14487-6-pkshih@realtek.com