rt2x00: Merge rt2x00ht.c contents in other files.

The two functions that are in rt2x00ht.c can be much better placed
closer to the places where the call-sites of these functions are (one
in rt2x00config.c and one in rt2x00queue.c) allowing us to make these
functions static.
Also, conditional compilations doesn't seem to be necessary anymore as
802.11n support is quite common nowadays.

This makes the code a bit easier readable and searchable.

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>