wifi: rtw89: fw: parse firmware element of DIAG_MAC

wifi: rtw89: fw: parse firmware element of DIAG_MAC

The firmware element ID 28 is a set of rules to diagnose if MAC get
abnormal. The latter patch will use these rules via debugfs to know
the status.

The element contains rules with their textual messages shown as below:

   +------------------------------------+
   |                                    |
   |                +-----------+       |
   |                | rule_size |-------|----------+
   +----------------+-----------+-------+ --       |
   |             rule[0]                |   \      |
   |             rule[1]                |   |  <---+
   |                :                   |   /
   +------------------------------------+ --
   | msg[0]      msg[1]                 |  each msg has variable length
   |        msg[2]    msg[3] ...        |  (with address align 2)
   | ...                                |
   +------------------------------------+

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20251111022452.28093-3-pkshih@realtek.com