rtw89: 8852c: add trigger frame counter

Adding this allows us to maintain trigger frame statistics, which is
required for our CFO tracking decisions.

Signed-off-by: Po Hao Huang <phhuang@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/20220608113224.11193-3-pkshih@realtek.com