rt2x00: Clarify supported chipsets in Kconfig

As reported by Filipus Klutiero <chealer@gmail.com>,
the rt2x00 Kconfig entries should be updated with
specific chipset notifications.

This cleans up Kconfig by explicitly mentioning the
supported chipsets for each drivers, and uses the
same chipset family names as mentioned on the Ralink website.

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