linux-firmware: Add ordinary firmware for RTL8821AU device

This firmware was extracted from the 20210708 release of the vendor
driver for this device. The firmware corresponds with the latest
release by Realtek.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>

WHENCE

@@ -3226,6 +3226,7 @@ Licence: Redistributable. See LICENCE.rtlwifi_firmware.txt for details.
 Driver: rtw88 - Realtek 802.11ac WLAN driver for RTL8822BE and RTL8822CE
 
 Info: Sent to Larry Finger by Realtek engineer Yan-Hsuan Chuang <yhchuang@realtek.com>
+File: rtw88/rtw8821a_fw.bin
 File: rtw88/rtw8822b_fw.bin
 File: rtw88/rtw8822c_fw.bin
 File: rtw88/rtw8822c_wow_fw.bin

rtw88/README

@@ -19,6 +19,9 @@ except that the device cannot be waken from the wireless NICs.
 
 Currently supported devices with corresponding firmwares:
 
+RTL8821AU
+    rtw8821a_fw.bin
+
 RTL8822BE
     rtw8822b_fw.bin