rtw88: 8822c: add new RFE type 6

A new RFE type 6 of RTL8822CE is released, add it in the RFE type
definition.

Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200623072014.31631-1-yhchuang@realtek.com