rtw89: pci: allow to process RPP prior to TX BD

RPP is to report certain skb(s) can be freed, and TX BD indicates which
TX descriptors can be freed. Normally, TX BD is happened before RPP.
In low power mode, RPP can happen ahead, so change flow to handle this
case.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220421120903.73715-8-pkshih@realtek.com