wifi: rtw89: load RFK log format string from firmware file

To debug RFK (RF calibration) in firmware, it sends log via firmware C2H
events to driver with string format ID and four arguments. Load formatted
string from firmware file, and the string ID can get back its string. Then,
use regular print format to show the message.

This firmware element layout looks like

    +============================================+
    |  elm ID  | elm size | version  |           |
    +----------+----------+----------+-----------+
    |                     | nr |rsvd |rfk_id|rsvd|
    +--------------------------------------------+
    | offset[] (__le16 * nr)                     |
    | ...                                        |
    +--------------------------------------------+
    | formatted string with null termintor (*nr) |
    | ...                                        |
    +============================================+

 * a firmware file can contains more than one elements with this element ID
   named RTW89_FW_ELEMENT_ID_RFKLOG_FMT (19), because many RFK needs its
   own formatted strings, so add 'rfk_id' to know it belongs to which RFK.
 * the 'formatted string' just follow 'offset[]' without padding to align
   32bits.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231213005054.10568-4-pkshih@realtek.com