rt2x00: Enabled rt35xx device support by default.

Now that support for these devices has been added we can enable them
by default and remove the Kconfig not on support for these devices to
be non-functional.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>