wifi: rtl8xxxu: Support new chip RTL8188FU

This chip is found in the cheapest USB adapters, e.g. 1.17 USD with
VAT and shipping from China included.

It's a gen 2 chip, similar to the RTL8723BU, but without Bluetooth.
Features: 2.4 GHz, b/g/n mode, 1T1R, 150 Mbps.

The vendor driver rtl8188fu version 4.3.23.6_20964.20170110 [0]
was used as reference. The CD shipped with the device includes a
newer driver, version 5.11.5-1-g12f7cde4b.20201102, but that one
couldn't complete the WPA2 key exchange thing for whatever reason.

[0] https://github.com/kelebek333/rtl8188fu

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/b14f299d-3248-98fe-eee1-ba50d2e76c74@gmail.com