rt2x00: Cleanup mode registration

Don't wildly pass any number for num_rates to rt2x00lib,
instead pass which type of rates are supported (CCK, OFDM).
Same for num_modes but then for the 2GHZ and 5GHZ band.

This makes the interface look much nicer and makes
extending it later easier.

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