rt2x00: Add new RF chip defines

Add new defines for RF chipsets which can be found
by the driver. We don't have to check for these
chips specifically yet, but it is better to have
the defines in now.

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