wifi: rtw89: add chip_info::txwd_info size to generalize TX WD submit

For existing chips, size of TX WD info is 6 words, but upcoming WiFi 7
chips become 8 words, so add a chip_info to reuse the code.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230911082049.33541-5-pkshih@realtek.com