wifi: rtw88: Add definitions for 8703b chip

default_cck_index is used in power track, the rx_cck_agc_report_type
for RX PHY status. GET_RX_DESC_BW is an RX descriptor field not used
by the other chip drivers.

Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Tested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Fiona Klute <fiona.klute@gmx.de>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240311103735.615541-4-fiona.klute@gmx.de