Add TP-Link TL-WN722N wifi usb adaptor

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Curiously there is a package rtl-8188-eu-firmware available, containing the binary blob to operate the device.

But the driver itself has apparently not yet made it to the master branch:

Support for 8188eu?

The firmware is available (rtl8188eu-firmware) but there are no drivers available to support it on OpenWrt's repos. 8188eu was supported with the rtl8xxxu driver on 17.01 but after this commit https://github.com/openwrt/openwrt/commit/66c5696cdf9599ccef652a651f52c0f7f53da44a the patches that made 8188eu work were dropped. Any hints I could follow to make it work ?