rtlwifi: rtl_pci: Add fill_tx_special_desc to issue H2C data, and process TXOK in interrupt.

With the RTL8822BE, an H2C tx queue is added to download FW and special
data. This change implements the support code in rtl_pci.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Cc: Birming Chiu <birming@realtek.com>
Cc: Shaofu <shaofu@realtek.com>
Cc: Steven Ting <steventing@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>