staging: r8712u: Add the new driver to the mainline kernel

This code is for a completely new version of the Realtek 8192 USB devices
such as the D-Link DWA-130. The Realtek code, which was originally for
Linux, Windows XP and Windows CE, has been stripped of all code not needed
for Linux. In addition, only one additional configuration variable, which
enables AP mode, remains.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Florian Schilhabel <florian.c.schilhabel@googlemail.com>
Tested-by: Frederic Leroy <fredo@starox.org>