rtw88: add rtw_fw_feature_check api

add api to check if a certain feature is supported.

Signed-off-by: Chin-Yen Lee <timlee@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210514075517.14216-2-pkshih@realtek.com