RK3326: enable the in-tree MT7921U driver with its firmware

Common WiFi 6 dongles use the MediaTek MT7921U, which mainline has
supported since 5.18, but the kernel config never enabled the USB
glue and the firmware list did not ship the MT7961 blobs. Cheapest
gap found in the four-distro dongle driver census.

projects/ArchR/devices/RK3326/linux/linux.aarch64.conf

@@ -2173,7 +2173,7 @@ CONFIG_MT7663_USB_SDIO_COMMON=m
 CONFIG_MT7663U=m
 CONFIG_MT7663S=m
 # CONFIG_MT7921S is not set
-# CONFIG_MT7921U is not set
+CONFIG_MT7921U=m
 # CONFIG_MT7925U is not set
 CONFIG_WLAN_VENDOR_MICROCHIP=y
 # CONFIG_WILC1000_SDIO is not set

projects/ArchR/packages/linux-firmware/kernel-firmware/firmwares/any.dat

@@ -14,6 +14,8 @@ mt7601u.bin
 mt7662*.bin
 mediatek/mt7662u*.bin
 mediatek/mt7610u.bin
+mediatek/WIFI_MT7961_patch_mcu_1_2_hdr.bin
+mediatek/WIFI_RAM_CODE_MT7961_1.bin
 
 ath6k/AR6004/hw1.?/bdata.bin
 ath9k_htc/*