linux-firmware: Package RSI 911x WiFi firmware

The RSI 911x WiFi firmware is already part of the linux-firmware
repository, package it to make it easily available.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit cc44b71f)
Signed-off-by: Steve Sakoman <steve@sakoman.com>