rtw89: ser: dump fw backtrace while L2 reset

Read FW backtrace entry through FW reserved payload engine, and then
add FW backtrace dump during SER (system error recover) L2 reset process.
It contains a list of RA (return address) and SP (stack pointer) which
gives us a chance to trace back the call stack of FW.

Moreover, if core dump might have wrong content due to error during
dumping, we won't invoke device core dump framework. For this case,
rtw89_ser_cd_free() is added to free buffer by ourselves.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220314071250.40292-7-pkshih@realtek.com