Staging: add rt3090 wireless driver

This is the vendor driver for the Ralink RT3090 chipset.

It should be later cleaned and ported to use the existing rt2x00
infrastructure or just replaced by the proper version.

[ Unfortunately since it follows the same design/implementation like
  rt{286,287,307}0 drivers (already present in the staging tree)
  it is highly unlikely that it will see much love from the wireless
  development community.. ]

However since the development of the cleaner/proper version can take
significant time lets give distros (i.e. openSUSE seems to already
have the package with the original vendor driver) and users "something"
to use in the meantime.

I forward ported it to 2.6.31-rc1, ported to the Linux build system
and did some initial cleanups.  More fixes/cleanups to come later
(it seems that the driver can be made to share most of its code with
the other Ralink drivers already present in the staging tree).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>